Clip the transformed and rounded sourceClip to the source rectangle,
so we don't try to rotate pixels outside the source.
Task-number: QTBUG-56252
Change-Id: Ib9cb80f9856724118867aea37ead0b02a6c71495
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>