fix(ui): send multigrid message position and size when the UI is refreshed

src/nvim/message.c

@@ -2521,6 +2521,14 @@ void msg_reset_scroll(void)
   msg_grid_scroll_discount = 0;
 }
 
+void msg_ui_refresh(void)
+{
+  if (ui_has(kUIMultigrid) && msg_grid.chars) {
+    ui_call_grid_resize(msg_grid.handle, msg_grid.cols, msg_grid.rows);
+    ui_ext_msg_set_pos(msg_grid_pos, msg_scrolled);
+  }
+}
+
 /// Increment "msg_scrolled".
 static void inc_msg_scrolled(void)
 {

src/nvim/ui.c

@@ -229,6 +229,7 @@ void ui_refresh(void)
     }
     msg_scroll_flush();
   }
+  msg_ui_refresh();
 
   if (!ui_active()) {
     return;