GLTF: Fix export_post_convert not running for multi-root scenes

modules/gltf/gltf_document.cpp

@@ -8552,18 +8552,16 @@ Error GLTFDocument::append_from_scene(Node *p_node, Ref<GLTFState> p_state, uint
 	// Add the root node(s) and their descendants to the state.
 	if (_root_node_mode == RootNodeMode::ROOT_NODE_MODE_MULTI_ROOT) {
 		const int child_count = p_node->get_child_count();
-		if (child_count > 0) {
-			for (int i = 0; i < child_count; i++) {
-				_convert_scene_node(state, p_node->get_child(i), -1, -1);
-			}
-			state->scene_name = p_node->get_name();
-			return OK;
+		for (int i = 0; i < child_count; i++) {
+			_convert_scene_node(state, p_node->get_child(i), -1, -1);
 		}
+		state->scene_name = p_node->get_name();
+	} else {
+		if (_root_node_mode == RootNodeMode::ROOT_NODE_MODE_SINGLE_ROOT) {
+			state->extensions_used.append("GODOT_single_root");
+		}
+		_convert_scene_node(state, p_node, -1, -1);
 	}
-	if (_root_node_mode == RootNodeMode::ROOT_NODE_MODE_SINGLE_ROOT) {
-		state->extensions_used.append("GODOT_single_root");
-	}
-	_convert_scene_node(state, p_node, -1, -1);
 	// Run post-convert for each extension, in case an extension needs to do something after converting the scene.
 	for (Ref<GLTFDocumentExtension> ext : document_extensions) {
 		ERR_CONTINUE(ext.is_null());