st/mesa: fix temp texture bindings in st_CopyPixels()

The temporary texture should have either PIPE_BIND_RENDER_TARGET or
PIPE_BIND_DEPTH_STENCIL set in addition to PIPE_BIND_SAMPLER_VIEW.

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Marek Olšák <maraeo@gmail.com>
glsl: Fix null check in read_dereference.

Fixes "Logically dead code" defect reported by Coverity.

Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Brian Paul <brianp@vmware.com>
ilo: silence a compiler warning

The path should never be hit.
ilo: add some assertions to help debugging

Assert that we do not support user vertex/index/constant buffers.  Issue a
warning when a sampler view is created for a resource without
PIPE_BIND_SAMPLER_VIEW.