Unbreak AJAX views using @get_path_obj

Since a81fa7b8f477eb9ab4b2bd8b9cacfdcc8630b566 @get_path_obj requires
that the request provide a ‘path’, but most of our AJAX requests do not
provide one, which breaks views that use @get_path_obj, so relax this
requirement and use the ‘path’ only when provided.