updated for version 7.2.370

Problem:    A redraw may cause folds to be closed.
Solution:   Revert part of the previous patch.  Add a test. (Lech Lorens)

src/option.c

@@ -6586,7 +6586,11 @@ did_set_string_option(opt_idx, varp, new_value_alloced, oldval, errbuf,
 		|| *curwin->w_p_fdm == NUL)
 	    errmsg = e_invarg;
 	else
+	{
 	    foldUpdateAll(curwin);
+	    if (foldmethodIsDiff(curwin))
+		newFoldLevel();
+	}
     }
 # ifdef FEAT_EVAL
     /* 'foldexpr' */