Fixed crash in QGraphicsWebView when clicking on links

The mouse event passed to this function is allocated on the stack, so
we can't delete it. Also, it doesn't make sense to allocate a new one
which immediately gets leaked. The intent must have been to use the ev
parameter as a return parameter - that's what it looks like on the
caller side.

Change-Id: I023cd7895a278eada4ad4acd233741aff837fed6
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>