... and avoid detach()ing potentially large data for just
preserving the QPlatformPixmap::pixelType().
A QBitmap differs from a QPixmap (its base class, urgh)
by always having a data != nullptr and a Bitmap pixel
type, yet load() was unconditionally setting 'data' to
nullptr on failure, turning a QBitmap into a non-QBitmap.
Fix by move-assigning a null QBitmap instead of resetting
'data'.
Add some tests.
Change-Id: Ida58b3b24d96472a5f9d0f18f81cc763edcf3c16
Reviewed-by: Anton Kudryavtsev <a.kudryavtsev@netris.ru>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
f9acbaccde