tree-wide: propagate the error we got from strv_extend_xyz() to the caller

It's a bit sloppy to return -ENOMEM rather than the actual error we
already returned in the first place (even though it's always going to be
ENOMEM)

src/core/manager-serialize.c

@@ -494,8 +494,9 @@ int manager_deserialize(Manager *m, FILE *f, FDSet *fds) {
                         (void) exec_shared_runtime_deserialize_one(m, val, fds);
                 else if ((val = startswith(l, "subscribed="))) {
 
-                        if (strv_extend(&m->deserialized_subscribed, val) < 0)
-                                return -ENOMEM;
+                        r = strv_extend(&m->deserialized_subscribed, val);
+                        if (r < 0)
+                                return r;
                 } else if ((val = startswith(l, "varlink-server-socket-address="))) {
                         if (!m->varlink_server && MANAGER_IS_SYSTEM(m)) {
                                 r = manager_varlink_init(m);