tree data BUGFIX check extensions with no plugins
diff --git a/src/tree_data_helpers.c b/src/tree_data_helpers.c
index fd773ab..2909f23 100644
--- a/src/tree_data_helpers.c
+++ b/src/tree_data_helpers.c
@@ -807,6 +807,11 @@
         nested_exts = sparent->exts;
     }
     LY_ARRAY_FOR(nested_exts, u) {
+        if (!nested_exts[u].def->plugin) {
+            /* no plugin */
+            continue;
+        }
+
         ext_snode_cb = nested_exts[u].def->plugin->snode;
         if (!ext_snode_cb) {
             /* not an extension with nested data */