rbt: fix incorrect replacement.

Author: dlbeer

src/rbt.c

@@ -213,6 +213,11 @@ struct rbt_node *rbt_insert(struct rbt *t, const void *key,
 
 		if (!r) {
 			memcpy(n, c, sizeof(*c));
+			*nptr = n;
+			if (n->left)
+				n->left->parent = n;
+			if (n->right)
+				n->right->parent = n;
 			return c;
 		}