vim-patch:8.2.0235: draw error when an empty group is removed from 'statusline'

Problem:    Draw error when an empty group is removed from 'statusline'.
Solution:   Do not use highlighting from a removed group.
dbe5d361fe

src/nvim/buffer.c

@@ -3531,6 +3531,12 @@ int build_stl_str_hl(
         if (n == curitem && group_start_userhl == group_end_userhl) {
           out_p = t;
           group_len = 0;
+          // do not use the highlighting from the removed group
+          for (n = groupitems[groupdepth] + 1; n < curitem; n++) {
+            if (items[n].type == Highlight) {
+              items[n].type = Empty;
+            }
+          }
         }
       }
 

src/nvim/testdir/test_statusline.vim

@@ -369,3 +369,24 @@ func Test_statusline_visual()
   bwipe! x1
   bwipe! x2
 endfunc
+
+func Test_statusline_removed_group()
+  if !CanRunVimInTerminal()
+    throw 'Skipped: cannot make screendumps'
+  endif
+
+  let lines =<< trim END
+    scriptencoding utf-8
+    set laststatus=2
+    let &statusline = '%#StatColorHi2#%(✓%#StatColorHi2#%) Q≡'
+  END
+  call writefile(lines, 'XTest_statusline')
+
+  let buf = RunVimInTerminal('-S XTest_statusline', {'rows': 10, 'cols': 50})
+  call term_wait(buf, 100)
+  call VerifyScreenDump(buf, 'Test_statusline_1', {})
+
+  " clean up
+  call StopVimInTerminal(buf)
+  call delete('XTest_statusline')
+endfunc