description:
"labels" button is not enabled until "show series labels" is tick.

build number:
2.6.0.v20100524-1222

steps to reproduce:
1. new a chart.
2. format chart->series->value (y) series.

expected result:
"curve fitting line" button is disabled when "show curve fitting line" is not tick.

actual result:
"labels" button is enabled when "show series labels" is not tick, but the operation in the dialogue does not take effect until "show series labels" is not tick.

error log:
n/a
this is expected behavior, and was added as an enhancement previously.
the data label settings are used not only in label text, but also in tooltips.
hence, even if data labels are invisible, user can use this ui to customize tooltips.
verified, closed.