Bug#622958: Mesa code is obviously broken

[Eric Valette <eric.valette@free.fr>]

Looking at mesa code I get this:

 struct intel_region *region = irb ? irb->region : NULL;

 brw_add_validated_bo(brw, region->buffer);

So  region may be set to null under cetain condition but is dereferenced 
the line after!

--eric