Fix tst_qgraphicsview::task255529_transformationAnchorMouseAndViewportMargins

Fix tst_qgraphicsview::task255529_transformationAnchorMouseAndViewportMargins

If we do not process the event, q->underMouse may return false in
QGraphicsViewPrivate::centerView (as the QEvent::Enter has not been
received yet.)

It was working before if by luck, the window appears under the cursor.

Change-Id: I9b4497683eae20915680297013a9c21fd6275f4b
Reviewed-on: http://codereview.qt.nokia.com/2385
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Sergio Ahumada <sergio.ahumada@nokia.com>