[GUI] Setting initial color of QColorDialog

[xtemp09]

This commit fixes issue #7322. When setting option the initial color is discarded. It needs to be reset, like it's done in void ColorButton::showModal().

Before

before.mp4

After

after.mp4

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[freecadci]

for feature branch PR_9287. Pipeline 838605566 was triggered at 1e16267. All CI branches and pipelines.

[chennes]

Looks great, thanks for those videos -- that's a very helpful way to show this sort of change.