fix(api): win_set_config update statuslines after removing splits

Problem: nvim_win_set_config does not update statuslines after removing a split.

Solution: call last_status.

Didn't realize this was missing in the original nvim_win_set_config for splits
PR.

As it can only be done for the current tabpage, do it if win_tp == curtab;
enter_tabpage will eventually call last_status anyway when the user enters
another tabpage.

src/nvim/api/win_config.c

@@ -550,6 +550,10 @@ void nvim_win_set_config(Window window, Dict(win_config) *config, Error *err)
       }
     }
     win_remove(win, win_tp == curtab ? NULL : win_tp);
+    if (win_tp == curtab) {
+      last_status(false);  // may need to remove last status line
+      win_comp_pos();  // recompute window positions
+    }
 
     int flags = win_split_flags(fconfig.split, parent == NULL) | WSP_NOENTER;
     TRY_WRAP(err, {

test/functional/api/window_spec.lua

@@ -2379,6 +2379,28 @@ describe('API/win', function()
       )
       eq(cur_win, api.nvim_get_current_win())
     end)
+
+    it('updates statusline when moving bottom split', function()
+      local screen = Screen.new(10, 10)
+      screen:set_default_attr_ids({
+        [0] = { bold = true, foreground = Screen.colors.Blue }, -- NonText
+        [1] = { bold = true, reverse = true }, -- StatusLine
+      })
+      screen:attach()
+      exec([[
+        set laststatus=0
+        belowright split
+        call nvim_win_set_config(0, #{split: 'above', win: win_getid(winnr('#'))})
+      ]])
+      screen:expect([[
+        ^            |
+        {0:~           }|*3
+        {1:[No Name]   }|
+                    |
+        {0:~           }|*3
+                    |
+      ]])
+    end)
   end)
 
   describe('get_config', function()