fold: fix a corner case. By Tomas Heinrich (heinrich.tomas AT gmail.com)

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

testsuite/fold.tests

@@ -0,0 +1,14 @@
+#!/bin/sh
+# Copyright 2009 by Denys Vlasenko
+# Licensed under GPL v2, see file LICENSE for details.
+
+. testing.sh
+
+# testing "test name" "options" "expected result" "file input" "stdin"
+
+testing "fold -s" "fold -w 7 -s" \
+	"123456\n\t\nasdf" \
+	"" \
+	"123456\tasdf" \
+
+exit $FAILCOUNT