QWindowVistaStyle: Always initialize text color of menu items.

[ChangeLog][QtWidgets][QMenu][Windows] Correctly use text color set by style sheet for menu items.

Task-number: QTBUG-36142

Change-Id: I142f2fd82164771b45bf599a6afa1121fcfd2187
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
(cherry picked from qtbase/b152b425f74788b2f2845fb7d1a5032d86b8746d)