input: Empty the current input region when configuring pointer surfaces

The input region of the cursor surface is set to empty in
pointer_cursor_surface_configure(). Since during the commit process
this function is called before the pending input region is made
current, it empties surface->pending.input instead of surface->input.

But pointer_cursor_surface_configure() is also called from
pointer_set_cursor() in order to map the cursor even if there isn't a
subsequent attach and commit to the cursor surface. In that case,
surface->input is never emptied, since the configure function emptied
only the pending input region and there wasn't a commit that made it
effective.

Fix this by emptying both pending and current input regions. The latter
shouldn't cause problems since the surface can't have a role prior to
being assigned the cursor role, so it shouldn't be mapped in the first
place.

Also change toytoolkit so that it triggers the bug.

https://bugs.freedesktop.org/show_bug.cgi?id=73711

clients/window.c

@@ -3458,13 +3458,13 @@ input_set_pointer_image_index(struct input *input, int index)
 	if (!buffer)
 		return;
 
-	wl_pointer_set_cursor(input->pointer, input->pointer_enter_serial,
-			      input->pointer_surface,
-			      image->hotspot_x, image->hotspot_y);
 	wl_surface_attach(input->pointer_surface, buffer, 0, 0);
 	wl_surface_damage(input->pointer_surface, 0, 0,
 			  image->width, image->height);
 	wl_surface_commit(input->pointer_surface);
+	wl_pointer_set_cursor(input->pointer, input->pointer_enter_serial,
+			      input->pointer_surface,
+			      image->hotspot_x, image->hotspot_y);
 }
 
 static const struct wl_callback_listener pointer_surface_listener;