Since c95b138 (Fix git-am safety checks, 2006-09-15), when there is a
session in progress, git-am will check the command-line arguments and
standard input to ensure that the user does not pass it any patches.
Add a test for this.
Reviewed-by: Stefan Beller <sbeller@google.com> Reviewed-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Paul Tan <pyokagan@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>