tree data BUGFIX schema mount merge

Author: Humblesaw

src/tree_data.c

@@ -688,10 +688,6 @@ lyd_insert_node_find_anchor(struct lyd_node *first_sibling, struct lyd_node *nod
 {
     struct lyd_node *anchor;
 
-    if (first_sibling && (first_sibling->flags & LYD_EXT)) {
-        return NULL;
-    }
-
     /* find the anchor, so we can insert somewhere before it */
     anchor = lyd_insert_get_next_anchor(first_sibling, node);
     /* cannot insert data node after opaque nodes */
@@ -767,7 +763,8 @@ lyd_insert_node(struct lyd_node *parent, struct lyd_node **first_sibling_p, stru
     }
     first_sibling = parent ? lyd_child(parent) : *first_sibling_p;
 
-    if ((order == LYD_INSERT_NODE_LAST) || !node->schema || (first_sibling && (first_sibling->flags & LYD_EXT))) {
+    if ((order == LYD_INSERT_NODE_LAST) || !node->schema ||
+            ((node->flags & LYD_EXT) && (!first_sibling || !(first_sibling->prev->flags & LYD_EXT)))) {
         lyd_insert_node_last(parent, &first_sibling, node);
     } else if (order == LYD_INSERT_NODE_LAST_BY_SCHEMA) {
         lyd_insert_node_ordby_schema(parent, &first_sibling, node);