uwac/input: Set the right serial when setting cursor

The serial in wl_pointer.set_cursor must exactly match the one from
wl_pointer.enter, it should not use whatever serial for any input class
is the newest.

uwac/libuwac/uwac-input.c

@@ -729,6 +729,7 @@ static void pointer_handle_enter(void* data, struct wl_pointer* pointer, uint32_
 	}
 
 	input->display->serial = serial;
+	input->display->pointer_focus_serial = serial;
 	window = wl_surface_get_user_data(surface);
 	if (window)
 		window->pointer_enter_serial = serial;
@@ -1191,5 +1192,5 @@ UwacReturnCode UwacSeatSetMouseCursor(UwacSeat* seat, const void* data, size_t l
 	}
 	if (seat && !seat->default_cursor)
 		return UWAC_SUCCESS;
-	return set_cursor_image(seat, seat->display->serial);
+	return set_cursor_image(seat, seat->display->pointer_focus_serial);
 }

uwac/libuwac/uwac-priv.h

@@ -121,6 +121,7 @@ struct uwac_display
 	bool running;
 	UwacTask dispatch_fd_task;
 	uint32_t serial;
+	uint32_t pointer_focus_serial;
 
 	struct wl_list windows;