surfaceless: Fix swrast-path segfault when loader doesn't know driver name.

If we're hitting the swrast fallback path here, it's probably because
we stumbled across a KMS-only device (such as the ASpeed that some of
our CI runners have) that will then return a NULL driver_name.  Don't
crash in that case.

Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
1 file changed