i965: Don't try to print the GLSL IR if it has been freed

i965: Don't try to print the GLSL IR if it has been freed

Since commit 104c8fc2c2aa5621261f8 the GLSL IR will be freed if NIR is
being used. This was causing it to segfault if INTEL_DEBUG=wm is set.
This patch just makes it avoid dumping the GLSL IR in that case.

Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>