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