daemon: guard NULL REMOTE_PORT in execute() logging

REMOTE_ADDR and REMOTE_PORT are both set by the same code path in
handle(), so when the existing REMOTE_ADDR check passes, REMOTE_PORT
is guaranteed to be non-NULL.  Guard REMOTE_PORT as well so that a
future change that breaks this invariant does not pass NULL to
printf's %s, which is undefined behavior.

Signed-off-by: Sebastien Tardif <sebtardif@ncf.ca>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

daemon.c

diff --git a/daemon.c b/daemon.c
index 103c08d..78cca86 100644
--- a/daemon.c
+++ b/daemon.c
@@ -753,7 +753,7 @@ static int execute(void)
 	struct strvec env = STRVEC_INIT;
 
 	if (addr)
-		loginfo("Connection from %s:%s", addr, port);
+		loginfo("Connection from %s:%s", addr, port ? port : "?");
 
 	set_keep_alive(0);
 	alarm(init_timeout ? init_timeout : timeout);