i965/fs: Fix segfault when using INTEL_DEBUG=perf with non-GLSL.

i965/fs: Fix segfault when using INTEL_DEBUG=perf with non-GLSL.

Now that ARB programs and fixed function are routed through the new
backend, shader might be NULL.  Don't do INTEL_DEBUG=perf support in
that case, since it relies on shader->compiled_once.

Since INTEL_DEBUG=perf wasn't previously supported, this maintains the
status quo.  It might be nice to support it someday, however.

This could be moved to brw_shader_program instead of brw_shader, but
it appears even prog can be NULL in that case.

Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>