playlist: Recurse on ITEM_TYPE_NODE when calculating the duration

When adding an item X whose underlying input_item_t's i_type is
ITEM_TYPE_NODE (like a folder), we need to call playlist_GetNodeDuration
on X again for the duration of X to be the sum of the durations of X's
children.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

src/playlist/item.c

@@ -733,7 +733,13 @@ mtime_t playlist_GetNodeDuration( playlist_item_t* node )
 
     if( node->i_children != -1 )
         for( int i = 0; i < node->i_children; i++ )
-            mt_duration += input_item_GetDuration( node->pp_children[i]->p_input );
+        {
+            input_item_t* p_input = node->pp_children[i]->p_input;
+            if ( p_input->i_type == ITEM_TYPE_NODE )
+                mt_duration += playlist_GetNodeDuration( node->pp_children[i] );
+            else
+                mt_duration += input_item_GetDuration( p_input );
+        }
 
     return mt_duration;
 }