tree: Avoid dereferencing nvme_subsystem_t before its check for NULL

Author: tbzatek

src/nvme/tree.c

@@ -1023,11 +1023,12 @@ nvme_ctrl_t nvme_lookup_ctrl(nvme_subsystem_t s, const char *transport,
 			     const char *host_iface, const char *trsvcid,
 			     nvme_ctrl_t p)
 {
-	nvme_root_t r = s->h ? s->h->r : NULL;
+	nvme_root_t r;
 	struct nvme_ctrl *c;
 
 	if (!s || !transport)
 		return NULL;
+	r = s->h ? s->h->r : NULL;
 	c = p ? nvme_subsystem_next_ctrl(s, p) : nvme_subsystem_first_ctrl(s);
 	for (; c != NULL; c = nvme_subsystem_next_ctrl(s, c)) {
 		if (strcmp(c->transport, transport))