send-email: send_message die on $!, not $?

If close fails we want to emit errno, not the return code of whatever
happened to be the child process run.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.comReviewed-by: Avery Pennarun <apenwarr@gmail.com>
Reviewed-by: Jeff King <peff@peff.net>
>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-send-email.perl

@@ -1035,7 +1035,7 @@ X-Mailer: git-send-email $gitversion
 			exec($smtp_server, @sendmail_parameters) or die $!;
 		}
 		print $sm "$header\n$message";
-		close $sm or die $?;
+		close $sm or die $!;
 	} else {
 
 		if (!defined $smtp_server) {