drm/xe: Protect against unset LRC when pausing submissions

drm/xe: Protect against unset LRC when pausing submissions

While pausing submissions, it is possible to encouner an exec queue
which is during creation, and therefore doesn't have a valid xe_lrc
struct reference.

Protect agains such situation, by checking for NULL before access.

Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Fixes: c25c1010df88 ("drm/xe/vf: Replay GuC submission state on pause / unpause")
Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20251124222853.1900800-1-tomasz.lis@intel.com
(cherry picked from commit 07cf4b864f523f01d2bb522a05813df30b076ba8)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>