Make wayland clients render when only visible from mirrors

Under some circumstances we can defer frame callbacks forever for clients
that are only visible on desk mirrors.

I'm not certain those circumstances should actually occur (Ref T5678) but
at least for now this is a trivial and harmless workaround.

Fix T5654

src/bin/e_comp_object.c

@@ -925,6 +925,19 @@ _e_comp_object_mirror_pixels_get(void *data, Evas_Object *obj)
         return;
      }
 
+   /* This is a big fat hack - ideally we're already on this list
+    * if the parent is visible, but there are some circumstances
+    * where a client receives damage while visible but its own pixels_get
+    * callback doesn't fire (new damage during the start frame of a desk
+    * switch animation).
+    * Thus we can't make this addition conditional on visibility or we can
+    * (under wayland at least) lose a frame callback and stop updating.
+    *
+    * e_comp_client_post_update_add() prevents clients from being
+    * on the list twice, so this is theoretically not harmful.
+    */
+   e_comp_client_post_update_add(ec);
+
    if (cw->native) return;
 
    evas_object_image_data_set(obj, e_pixmap_image_data_get(cw->ec->pixmap));