mesa: Add error condition for format=STENCIL_INDEX in glGetTexImage()
From OpenGL 4.0 spec, page 306: "Calling GetTexImage with a format of STENCIL_INDEX causes the error INVALID_ENUM." Cc: <mesa-stable@lists.freedesktop.org> Signed-off-by:Anuj Phogat <anuj.phogat@gmail.com> Reviewed-by:
Ian Romanick <ian.d.romanick@intel.com> (cherry picked from commit 5388fc15)