Commit e459c8bf added a sanity check to prevent recomputing the texture matrix if the y-inverted hint hasn't been changed, which is totally reasonable!
However, code that initializes dmabuf textures implicitly assumes that calling setYInverted() always results in updating the matrix. But it may be not the case if the passed value matches current isYInverted().
This change adds missing calls to force updating the texture matrix.
Note that we don't need to check the buffer size every time the dmabuf image has been modified externally because the window pixmap is going to be re-created if the dimensions of the attached buffer have been changed.
I've seen some reports on the internet about Firefox displaying garbage instead of videos. 99% that bug is caused by this issue. But it seems like Firefox no longer displays corrupted videos on my machine, so it's hard to tell.