mesa: fix glTexImage proxy texture error generation

mesa: fix glTexImage proxy texture error generation

When calling glTexImage() with a proxy target most error conditions should
generate a GL error.  We were erroneously doing the proxy-error behaviour
(where we zeroed-out the image's width/height/depth/format fields) in too
many places.

There's another issue with proxy textures, but that'll be fixed in the
next patch.

Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>