git-svn: don't attempt to spawn pager if we don't want one

Even though config_pager() unset the $pager variable, we were
blindly calling exec() on it through run_pager().

Noticed-by: Chris Moore <christopher.ian.moore@gmail.com>
Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-svn.perl

@@ -3576,7 +3576,7 @@ sub config_pager {
 }
 
 sub run_pager {
-	return unless -t *STDOUT;
+	return unless -t *STDOUT && defined $pager;
 	pipe my $rfd, my $wfd or return;
 	defined(my $pid = fork) or ::fatal "Can't fork: $!\n";
 	if (!$pid) {