patch 8.2.4935: with 'foldmethod' "indent" some lines not included in fold

Problem:    With 'foldmethod' "indent" some lines are not included in the
            fold. (Oleg Koshovetc)
Solution:   Fix it. (Brandon Simmons, closes #10399, closes #3214)
diff --git a/src/testdir/test_fold.vim b/src/testdir/test_fold.vim
index 3abb81a..52185dc 100644
--- a/src/testdir/test_fold.vim
+++ b/src/testdir/test_fold.vim
@@ -1459,4 +1459,24 @@
   bw!
 endfunc
 
+" Make sure that when you append under a blank line that is under a fold with
+" the same indent level as your appended line, the fold expands across the
+" blank line
+func Test_indent_append_under_blank_line()
+  new
+  let lines =<< trim END
+    line 1
+      line 2
+      line 3
+  END
+  call setline(1, lines)
+  setlocal sw=2
+  setlocal foldmethod=indent foldenable
+  call assert_equal([0, 1, 1], range(1, 3)->map('foldlevel(v:val)'))
+  call append(3, '')
+  call append(4, '  line 5')
+  call assert_equal([0, 1, 1, 1, 1], range(1, 5)->map('foldlevel(v:val)'))
+  bw!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab