svga: add null ptr check in svga_get_tex_sampler_view()

Trivial.
svga: minor cleanups, comments in svga_tgsi_insn.c
gallium/docs: more documentation for pipe_resource::array_size

It should never be zero and for cube/cube_arrays it should be a
multiple of six.

Reviewed-by: Roland Scheidegger <sroland@vmware.com>
llvmpipe: fix wrong results for queries not in a scene

The result isn't always 0 in this case (depends on query type),
so instead of special casing this just use the ordinary path (should result
in correct values thanks to initialization in query_begin/end), just
skipping the fence wait.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>