fix(ui2): ensure msg window is visible after closing tab

Problem:  After closing a tabpage while the msg window is showing a
          message, it is hidden while the msg window still contains a
          message.
Solution: Unhide the msg window after entering a tabpage and it still
          contains a message.

Co-authored-by: Linykq <yukunlin590@gmail.com>

runtime/lua/vim/_core/ui2.lua

@@ -239,8 +239,12 @@ function M.enable(opts)
 
   api.nvim_create_autocmd({ 'VimResized', 'TabEnter' }, {
     group = M.augroup,
-    callback = function()
+    callback = function(ev)
       M.check_targets()
+      -- After a tabpage was closed unhide the msg window on the current tabpage.
+      if ev.event == 'TabEnter' and next(M.msg.msg.ids) ~= nil then
+        api.nvim_win_set_config(M.wins.msg, { hide = false, width = M.msg.msg.width })
+      end
       M.msg.set_pos()
     end,
     desc = 'Set cmdline and message window dimensions after shell resize or tabpage change.',