Default to Qt::ArrowCursor when cursor = 0 in changeCursor().
Default to Qt::ArrowCursor when cursor = 0 in changeCursor().

The planned fix for the task introduces passing cursor = 0
meaning "no cursor set" for the window in question. Prevent
it from crashing by defaulting to Qt::ArrowCursor.

Task-number: QTBUG-28879
Change-Id: I3233c79d41ccf96cee237d93624b3ea740b7e772
Reviewed-by: Pier Luigi Fiorini <295fa01708b2fee29c68701c2be812b51a3cff23@gmail.com>
Reviewed-by: Andy Nichols <3d1e63b963f99f97839545621c6a9a8e2b2ab8fd@digia.com>

locusf/qtwayland-1,locusf/qtwayland-1,locusf/qtwayland-1,ntanibata/qtwayland,ntanibata/qtwayland,Tofee/qtwayland,locusf/qtwayland-1,Tofee/qtwayland,Tofee/qtwayland,ntanibata/qtwayland