mesa/st: Finalize the texture before BlitFramebuffer from it.

If the texture hasn't yet been validated, the current tex image contents
may have been ignored in favor of the texture's main miptree.  Fixes test
failure on softpipe and intermittent failures on radeonsi in:

https://gitlab.freedesktop.org/mesa/piglit/-/merge_requests/428

Cc: mesa-stable
Tested-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8091>
(cherry picked from commit f740af27964ef148de94fd389edf736bb488bfd0)
2 files changed