send-email: do not leave an empty CC: line if no cc is present.

Signed-off-by: Junio C Hamano <junkio@cox.net>

git-send-email.perl

@@ -446,9 +446,12 @@ sub send_message
 		my ($name, $addr) = ($from =~ /^(.*?)(\s+<.*)/);
 		$from = "\"$name\"$addr";
 	}
+	my $ccline = "";
+	if ($cc ne '') {
+		$ccline = "\nCc: $cc";
+	}
 	my $header = "From: $from
-To: $to
-Cc: $cc
+To: $to${ccline}
 Subject: $subject
 Date: $date
 Message-Id: $message_id