Cleanup the QtWidgets animation examples:
- use nullptr
- use normalized includes, remove unused includes
- fix style
- fix crash of sub-attaq when the game ended (error during range-based
for loop porting)
- don't use keyword 'final' for a variable name
Change-Id: Id23be8ff8b1b310da005d13c052fe547f6a0d63a
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>