mesa/texgetimage: fix missing stencil check
mesa/texgetimage: fix missing stencil check

GetTexImage can read to stencil8 but only from
a stencil or depthstencil textures.

This fixes a bunch of failures in CTS
GL33-CTS.gtf32.GL3Tests.packed_pixels

Reviewed-by: Marek Olšák <8c7344a1abdb103e79ecfd488098373070c3c70e@amd.com>
Cc: "11.0" <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>
Signed-off-by: Dave Airlie <f2295d84e358395675bc8031be58672073ae065e@redhat.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler