If `WARN_ON(!glob)` is ever triggered, we will still continue executing
the next lines. This will trigger the more serious problem, a NULL
pointer dereference bug.

Just return -EINVAL if @glob is NULL.

Link: https://lkml.kernel.org/r/20220417185630.199062-2-ammarfaizi2@gnuweeb.org

Cc: Ingo Molnar <mingo@redhat.com>
Cc: GNU/Weeb Mailing List <gwml@vger.gnuweeb.org>
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>