bisect: check for mandatory argument of 'bisect replay'

'git bisect replay' has a mandatory logfile argument, but the current
implementation doesn't check whether the user has specified one.  When
the user omits the logfile argument, this leads to the following
unhelpful error message:

  cannot read  for replaying

So, check for the mandatory argument first, and provide a more
meaningful error message when it is omitted.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-bisect.sh

@@ -343,6 +343,7 @@ bisect_clean_state() {
 }
 
 bisect_replay () {
+	test "$#" -eq 1 || die "No logfile given"
 	test -r "$1" || die "cannot read $1 for replaying"
 	bisect_reset
 	while read git bisect command rev