patch 8.2.1947: crash when using "zj" without folds

Problem:    Crash when using "zj" without folds. (Sean Dewar)
Solution:   Check for at least one fold. (closes #7245)

Author: brammool

src/fold.c

@@ -902,6 +902,8 @@ foldMoveTo(
 	// that moves the cursor is used.
 	lnum_off = 0;
 	gap = &curwin->w_folds;
+	if (gap->ga_len == 0)
+	    break;
 	use_level = FALSE;
 	maybe_small = FALSE;
 	lnum_found = curwin->w_cursor.lnum;

src/testdir/test_fold.vim

@@ -835,4 +835,13 @@ func Test_undo_fold_deletion()
   bwipe!
 endfunc
 
+" this was crashing
+func Test_move_no_folds()
+  new
+  fold
+  setlocal fdm=expr
+  normal zj
+  bwipe!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1947,
 /**/
     1946,
 /**/