patch 8.2.5009: fold may not be closeable after appending

Problem:    Fold may not be closeable after appending.
Solution:   Set the fd_small flag to MAYBE. (Brandon Simmons, closes #10471)

src/fold.c

@@ -2574,6 +2574,7 @@ foldUpdateIEMSRecurse(
 					(long)(fp->fd_top - firstlnum));
 			    fp->fd_len += fp->fd_top - firstlnum;
 			    fp->fd_top = firstlnum;
+			    fp->fd_small = MAYBE;
 			    fold_changed = TRUE;
 			}
 			else if ((flp->start != 0 && lvl == level)

src/testdir/test_fold.vim

@@ -1528,4 +1528,23 @@ func Test_indent_one_line_fold_close()
   bw!
 endfunc
 
+" Make sure that when appending [an indented line then a blank line] right
+" before a single indented line, the resulting extended fold can be closed
+func Test_indent_append_blank_small_fold_close()
+  new
+  setlocal sw=2 foldmethod=indent
+  " at first, the fold at the second line can't be closed since it's smaller
+  " than foldminlines
+  let lines =<< trim END
+    line 1
+      line 4
+  END
+  call setline(1, lines)
+  call append(1, ['  line 2', ''])
+  " close all folds
+  normal zM
+  call assert_notequal(-1, foldclosed(2)) " the fold should be closed now
+  bw!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -734,6 +734,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    5009,
 /**/
     5008,
 /**/