nvme_round_robin_path() should test if the return ns pointer is valid.
nvme_next_ns() will return a NULL pointer if there is no path left.
Fixes: 75c10e732724 ("nvme-multipath: round-robin I/O policy")
Signed-off-by: Daniel Wagner <dwagner@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
        }
 
        for (ns = nvme_next_ns(head, old);
-            ns != old;
+            ns && ns != old;
             ns = nvme_next_ns(head, ns)) {
                if (nvme_path_is_disabled(ns))
                        continue;