clients/window: fail earlier when frame_create fails

This adds a new NULL check to fail earlier when frame_create fails. This can
happen because PNG files couldn't be loaded from the data directory.

Signed-off-by: Simon Ser <contact@emersion.fr>

clients/window.c

@@ -2577,6 +2577,10 @@ window_frame_create(struct window *window, void *data)
 	frame = xzalloc(sizeof *frame);
 	frame->frame = frame_create(window->display->theme, 0, 0,
 	                            buttons, window->title, NULL);
+	if (!frame->frame) {
+		free(frame);
+		return NULL;
+	}
 
 	frame->widget = window_add_widget(window, frame);
 	frame->child = widget_add_widget(frame->widget, data);