input: Check device counts in bind_seat()

We shouldn't be using seat->pointer|keyboard|touch here, we should be
testing *_device_count to see if a device is currently present.

Testing the pointers directly will result in incorrectly advertising
capabilities after all devices of a type have been removed.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Jonas Ådahl <jadahl@gmail.com>

src/input.c

@@ -1901,11 +1901,11 @@ bind_seat(struct wl_client *client, void *data, uint32_t version, uint32_t id)
 	wl_resource_set_implementation(resource, &seat_interface, data,
 				       unbind_resource);
 
-	if (seat->pointer)
+	if (seat->pointer_device_count)
 		caps |= WL_SEAT_CAPABILITY_POINTER;
-	if (seat->keyboard)
+	if (seat->keyboard_device_count)
 		caps |= WL_SEAT_CAPABILITY_KEYBOARD;
-	if (seat->touch)
+	if (seat->touch_device_count)
 		caps |= WL_SEAT_CAPABILITY_TOUCH;
 
 	wl_seat_send_capabilities(resource, caps);