meta/copy_image: Stash off the scissor

meta/copy_image: Stash off the scissor

The meta CopyImageSubData path uses BlitFramebuffers to do the actual copy.
The only thing that can affect BlitFramebuffers other than the currently
bound framebuffers is the scissor so we need to save that off and reset it.
If we don't do this, applications that use a scissor together with
CopyImageSubData will get accidentally scissored copies.

Tested-by: Markus Wick <markus at selfnet.de>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>