minor findnode optimization

when searching the cache for a node so that we can delete an
rdataset, it is not necessary to set the 'create' flag. if the
node doesn't exist yet, we then we won't be able to delete
anything from it anyway.

(cherry picked from commit 6b720bfe1a)

lib/dns/resolver.c

@@ -5220,7 +5220,7 @@ validated(void *arg) {
 			result = ISC_R_NOTFOUND;
 			if (val->rdataset != NULL) {
 				result = dns_db_findnode(fctx->cache, val->name,
-							 true, &node);
+							 false, &node);
 			}
 			if (result == ISC_R_SUCCESS) {
 				(void)dns_db_deleterdataset(fctx->cache, node,
@@ -5858,7 +5858,6 @@ cache_name(fetchctx_t *fctx, dns_name_t *name, dns_message_t *message,
 	/*
 	 * Find or create the cache node.
 	 */
-	node = NULL;
 	result = dns_db_findnode(fctx->cache, name, true, &node);
 	if (result != ISC_R_SUCCESS) {
 		return (result);