bcachefs: Fix assertion in topology repair

If we were at the end of the node, when breaking out of the loop we'd
pop the assertion on line 446 when cur wasn't NULL.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/btree_gc.c

@@ -395,6 +395,7 @@ static int bch2_btree_repair_topology_recurse(struct bch_fs *c, struct btree *b)
 			bch2_btree_node_evict(c, cur_k.k);
 			ret = bch2_journal_key_delete(c, b->c.btree_id,
 						      b->c.level, cur_k.k->k.p);
+			cur = NULL;
 			if (ret)
 				break;
 			continue;
@@ -413,6 +414,7 @@ static int bch2_btree_repair_topology_recurse(struct bch_fs *c, struct btree *b)
 			bch2_btree_node_evict(c, cur_k.k);
 			ret = bch2_journal_key_delete(c, b->c.btree_id,
 						      b->c.level, cur_k.k->k.p);
+			cur = NULL;
 			if (ret)
 				break;
 			continue;