elementary: clear callbacks before destroying object to avoid crash.

@fix

T3188

src/lib/elementary/elm_gengrid.c

@@ -4116,6 +4116,7 @@ _internal_elm_gengrid_clear(Evas_Object *obj,
 
              if (next) itn = ELM_GEN_ITEM_FROM_INLIST(next);
              if (itn) itn->walking++;  /* prevent early death of subitem */
+             _item_mouse_callbacks_del(it, VIEW(it));
              it->del_cb(it);
              eo_del(EO_OBJ(it));
              if (itn) itn->walking--;