QToolTip does not correctly resize if a CSS style sheet is used and the font size is changed

If a widget uses a CSS style sheet (via setStyleSheet) which changes the font size of QToolTip (or of a basse class, e.g. QWidget),
then a QToolTip shown on that widget will calculate a wrong size, so that the text does not fit.

The QToolTip code resizes to a wrong size because it uses the QApplication::font("QToolTip") method to detect the font
instead of using the CSS style. The rendering takes the style sheet into account and thus the text does not fit in the QToolTip anymore.

The reason for this is that the CSS style is taken over too late, it has to be set on QToolTip label BEFORE resizing, otherwise the style sheet does not affect the resizing.

I attached a patch which fixes the problem.