server: Require a directory as root to open an object with a name.

server/handle.c

@@ -592,7 +592,14 @@ obj_handle_t open_object( struct process *process, obj_handle_t parent, unsigned
         return 0;
     }
 
-    if (parent && !(root = get_handle_obj( process, parent, 0, NULL ))) return 0;
+    if (parent)
+    {
+        if (name->len)
+            root = get_directory_obj( process, parent );
+        else  /* opening the object itself can work for non-directories too */
+            root = get_handle_obj( process, parent, 0, NULL );
+        if (!root) return 0;
+    }
 
     if ((obj = open_named_object( root, ops, name, attributes )))
     {