The missing case caused BitmapReadAccess to work with random data
(together with a follow-up bug that didn't deallocate data properly
after ReadTexture() failed).

Change-Id: I4546ee4ca85d6a0b01cc41636c257008c9f19587
Reviewed-on: https://gerrit.libreoffice.org/69745
Tested-by: Jenkins
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>