validation BUGFIX in ::lyd_validate_subtree()

Infinite loop due to opaq node that should be skipped.
diff --git a/src/validation.c b/src/validation.c
index d999a3f..6063c15 100644
--- a/src/validation.c
+++ b/src/validation.c
@@ -1460,7 +1460,7 @@
 
     LYD_TREE_DFS_BEGIN(root, node) {
         if (!node->schema) {
-            continue;
+            goto next_node;
         }
 
         LY_LIST_FOR(node->meta, meta) {
@@ -1487,6 +1487,7 @@
         }
         LY_CHECK_RET(lysc_node_ext_tovalidate(node_exts, node));
 
+next_node:
         LYD_TREE_DFS_END(root, node);
     }