mesa: fix assertion failure in TexImage
Check the assertion after error checking.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111194
Fixes: 9dd1f7ce
Check the assertion after error checking.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111194
Fixes: 9dd1f7ce