fix after static analysis

src/knot/dnssec/nsec-chain.c

@@ -295,7 +295,6 @@ int knot_nsec_chain_iterate_fix(zone_tree_t *old_nodes, zone_tree_t *new_nodes,
 		while (cmp != 0) {
 			if (cmp < 0) {
 				// a node was removed
-				old_prev = old_curr;
 				old_curr = it_next1(&old_it, old_first);
 				ret = callback(new_prev, new_curr, data);
 				CHECK_RET;

src/knot/zone/zone-tree.c

@@ -334,6 +334,11 @@ void zone_tree_it_free(zone_tree_it_t *it)
 int zone_tree_delsafe_it_begin(zone_tree_t *tree, zone_tree_delsafe_it_t *it)
 {
 	it->total = zone_tree_count(tree);
+	if (it->total == 0) {
+		it->current = 0;
+		it->nodes = NULL;
+		return KNOT_EOK;
+	}
 	it->nodes = malloc(it->total * sizeof(*it->nodes));
 	if (it->nodes == NULL) {
 		return KNOT_ENOMEM;