description:
[regression] exception throw out when delect xtab which extended from library [1102]

build:
<2.5.2.v20100210-0630>

steps to reproduce:
1. new a library with xtab
2. new a report and extend library's xtab
3. delete the xtab

actual result:
exception thrown out after step3

expect result:
no error

errorlog:
org.eclipse.birt.report.designer.core.runtime.guiexception: widget is disposed
	at org.eclipse.birt.report.designer.core.runtime.guiexception.createguiexception(guiexception.java:78)
	at org.eclipse.birt.report.designer.internal.ui.util.exceptionhandler.handle(exceptionhandler.java:169)
	at org.eclipse.birt.report.designer.internal.ui.util.exceptionhandler.handle(exceptionhandler.java:150)
	at org.eclipse.birt.report.designer.internal.ui.util.exceptionhandler.handle(exceptionhandler.java:89)
	at org.eclipse.birt.report.designer.internal.ui.editors.parts.event.modeleventmanager.postmodelevent(modeleventmanager.java:147)
	at org.eclipse.birt.report.designer.internal.ui.editors.parts.event.modeleventmanager.postevent(modeleventmanager.java:116)
	at org.eclipse.birt.report.designer.internal.ui.editors.parts.event.modeleventmanager.access$0(modeleventmanager.java:96)
	at org.eclipse.birt.report.designer.internal.ui.editors.parts.event.modeleventmanager$1.stackchanged(modeleventmanager.java:58)
	at org.eclipse.birt.report.model.activity.activitystack.sendnotifcations(activitystack.java:886)
	at org.eclipse.birt.report.model.activity.activitystack.commit(activitystack.java:756)
	at org.eclipse.birt.report.designer.internal.ui.command.wrappercommandstack.execute(wrappercommandstack.java:93)
	at org.eclipse.gef.ui.actions.workbenchpartaction.execute(workbenchpartaction.java:76)
	at org.eclipse.gef.ui.actions.deleteaction.run(deleteaction.java:125)
	at org.eclipse.birt.report.designer.internal.ui.editors.parts.graphicaleditorwithflyoutpalette$5.run(graphicaleditorwithflyoutpalette.java:415)
	at org.eclipse.jface.action.action.runwithevent(action.java:498)
	at org.eclipse.jface.commands.actionhandler.execute(actionhandler.java:119)
	at org.eclipse.core.commands.command.executewithchecks(command.java:476)
	at org.eclipse.core.commands.parameterizedcommand.executewithchecks(parameterizedcommand.java:508)
	at org.eclipse.ui.internal.handlers.handlerservice.executecommand(handlerservice.java:169)
	at org.eclipse.ui.internal.keys.workbenchkeyboard.executecommand(workbenchkeyboard.java:470)
	at org.eclipse.ui.internal.keys.workbenchkeyboard.press(workbenchkeyboard.java:824)
	at org.eclipse.ui.internal.keys.workbenchkeyboard.processkeyevent(workbenchkeyboard.java:880)
	at org.eclipse.ui.internal.keys.outoforderlistener.handleevent(outoforderlistener.java:76)
	at org.eclipse.swt.widgets.eventtable.sendevent(eventtable.java:84)
	at org.eclipse.swt.widgets.widget.sendevent(widget.java:1003)
	at org.eclipse.swt.widgets.widget.sendevent(widget.java:1027)
	at org.eclipse.swt.widgets.widget.sendevent(widget.java:1012)
	at org.eclipse.swt.widgets.widget.sendkeyevent(widget.java:1040)
	at org.eclipse.swt.widgets.widget.sendkeyevent(widget.java:1036)
	at org.eclipse.swt.widgets.widget.wmkeydown(widget.java:1669)
	at org.eclipse.swt.widgets.control.wm_keydown(control.java:4281)
	at org.eclipse.swt.widgets.control.windowproc(control.java:3977)
	at org.eclipse.swt.widgets.canvas.windowproc(canvas.java:342)
	at org.eclipse.swt.widgets.display.windowproc(display.java:4632)
	at org.eclipse.swt.internal.win32.os.dispatchmessagew(native method)
	at org.eclipse.swt.internal.win32.os.dispatchmessage(os.java:2411)
	at org.eclipse.swt.widgets.display.readanddispatch(display.java:3501)
	at org.eclipse.ui.internal.workbench.runeventloop(workbench.java:2405)
	at org.eclipse.ui.internal.workbench.runui(workbench.java:2369)
	at org.eclipse.ui.internal.workbench.access$4(workbench.java:2221)
	at org.eclipse.ui.internal.workbench$5.run(workbench.java:500)
	at org.eclipse.core.databinding.observable.realm.runwithdefault(realm.java:332)
	at org.eclipse.ui.internal.workbench.createandrunworkbench(workbench.java:493)
	at org.eclipse.ui.platformui.createandrunworkbench(platformui.java:149)
	at org.eclipse.ui.internal.ide.application.ideapplication.start(ideapplication.java:113)
	at org.eclipse.equinox.internal.app.eclipseapphandle.run(eclipseapphandle.java:194)
	at org.eclipse.core.runtime.internal.adaptor.eclipseapplauncher.runapplication(eclipseapplauncher.java:110)
	at org.eclipse.core.runtime.internal.adaptor.eclipseapplauncher.start(eclipseapplauncher.java:79)
	at org.eclipse.core.runtime.adaptor.eclipsestarter.run(eclipsestarter.java:368)
	at org.eclipse.core.runtime.adaptor.eclipsestarter.run(eclipsestarter.java:179)
	at sun.reflect.nativemethodaccessorimpl.invoke0(native method)
	at sun.reflect.nativemethodaccessorimpl.invoke(nativemethodaccessorimpl.java:39)
	at sun.reflect.delegatingmethodaccessorimpl.invoke(delegatingmethodaccessorimpl.java:25)
	at java.lang.reflect.method.invoke(method.java:585)
	at org.eclipse.equinox.launcher.main.invokeframework(main.java:559)
	at org.eclipse.equinox.launcher.main.basicrun(main.java:514)
	at org.eclipse.equinox.launcher.main.run(main.java:1311)
caused by: org.eclipse.swt.swtexception: widget is disposed
	at org.eclipse.swt.swt.error(swt.java:3884)
	at org.eclipse.swt.swt.error(swt.java:3799)
	at org.eclipse.swt.swt.error(swt.java:3770)
	at org.eclipse.swt.widgets.widget.error(widget.java:463)
	at org.eclipse.swt.widgets.widget.checkwidget(widget.java:336)
	at org.eclipse.swt.widgets.composite.layout(composite.java:545)
	at org.eclipse.birt.report.designer.internal.ui.views.attributes.section.togglessection.load(togglessection.java:118)
	at org.eclipse.birt.report.designer.internal.ui.views.attributes.page.attributepage.postelementevent(attributepage.java:259)
	at org.eclipse.birt.report.designer.internal.ui.editors.parts.event.modeleventmanager.postmodelevent(modeleventmanager.java:142)
	... 52 more
fixed.
verified.