QBranches::on_colorPB_clicked() one-line bug fix:

QBranches::on_colorPB_clicked() one-line bug fix:
When you click the "Alter button" on a added branch in "Document Settings/Branches" Dialog, clicking on the palette on the right to select a color won't work (selected color stays black). After selecting a color from the "Basic Colors" or the "Custon colors"
(which works fine), the color selection from the palette will work correctly. The problems lies in that the QColor() constructor produces an invalid color (RGB 0,0,0). "lightskyblue" is now the default color for a branch when you click the alter button.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@13429 a592a061-630c-0410-9148-cb99ea01b6c8