git-am: Do not exit silently if committer is unset

Signed-off-by: Stephan Beyer <s-beyer@gmx.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-am.sh

@@ -30,7 +30,8 @@ set_reflog_action am
 require_work_tree
 cd_to_toplevel
 
-git var GIT_COMMITTER_IDENT >/dev/null || exit
+git var GIT_COMMITTER_IDENT >/dev/null ||
+	die "You need to set your committer info first"
 
 stop_here () {
     echo "$1" >"$dotest/next"