Detect wrongly labelled wheel buttons

A mouse device with both missing labels and a wrongly placed label
on the mouse wheel buttons have been spotted.

This patch makes the XInput2 code even more lenient to better match
legacy systems that always assumed button 4 and 5 are mapped that way.

Task-number: QTBUG-40806
Change-Id: I7cc52f3d9c54e15e6f3ddcc2bdeb1bb8e0ac9eca
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>