messages: redraw tabline if it was overdrawn by messages

fixes #8354

Regression from #8088, where we try to avoid clearing the screen
if not absolutely necessary

src/nvim/screen.c

@@ -309,6 +309,9 @@ void update_screen(int type)
         if (wp->w_winrow + wp->w_height + wp->w_status_height > valid) {
           wp->w_redr_status = true;
         }
+        if (valid == 0) {
+          redraw_tabline = true;
+        }
       }
     } else if (msg_scrolled > Rows - 5) {  // clearing is faster
       type = CLEAR;

test/functional/ui/screen_basic_spec.lua

@@ -240,8 +240,8 @@ describe('Screen', function()
     end)
   end)
 
-  describe('tabnew', function()
+  describe('tabs', function()
-    it('creates a new buffer', function()
+    it('tabnew creates a new buffer', function()
       command('sp')
       command('vsp')
       command('vsp')
@@ -299,6 +299,62 @@ describe('Screen', function()
                                                              |
       ]])
     end)
+
+    it('tabline is redrawn after messages', function()
+      command('tabnew')
+      screen:expect([[
+        {4: [No Name] }{2: [No Name] }{3:                              }{4:X}|
+        ^                                                     |
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+                                                             |
+      ]])
+
+      feed(':echo "'..string.rep('x\\n', 11)..'"<cr>')
+      screen:expect([[
+        {1:                                                     }|
+        x                                                    |
+        x                                                    |
+        x                                                    |
+        x                                                    |
+        x                                                    |
+        x                                                    |
+        x                                                    |
+        x                                                    |
+        x                                                    |
+        x                                                    |
+        x                                                    |
+                                                             |
+        {7:Press ENTER or type command to continue}^              |
+      ]])
+
+      feed('<cr>')
+      screen:expect([[
+        {4: [No Name] }{2: [No Name] }{3:                              }{4:X}|
+        ^                                                     |
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+        {0:~                                                    }|
+                                                             |
+      ]])
+    end)
   end)
 
   describe('insert mode', function()