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)

src/fold.c

@@ -2246,7 +2246,14 @@ foldUpdateIEMS(win_T *wp, linenr_T top, linenr_T bot)
 	    getlevel = foldlevelDiff;
 #endif
 	else
+	{
 	    getlevel = foldlevelIndent;
+	    // Start one line back, because if the line above "top" has an
+	    // undefined fold level, folding it relies on the line under it,
+	    // which is "top".
+	    if (top > 1)
+		--fline.lnum;
+	}
 
 	// Backup to a line for which the fold level is defined.  Since it's
 	// always defined for line one, we will stop there.

src/testdir/test_fold.vim

@@ -1459,4 +1459,24 @@ func Test_fold_split()
   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

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4935,
 /**/
     4934,
 /**/