daemon: guard NULL REMOTE_PORT in execute() logging

daemon: guard NULL REMOTE_PORT in execute() logging

REMOTE_ADDR and REMOTE_PORT are both set by the same code path in
handle(), so neither should be NULL independently. However, the
existing code checks REMOTE_ADDR before the loginfo() call but not
REMOTE_PORT. If REMOTE_PORT were unset, NULL would be passed to
printf's %s, which is undefined behavior.

Add a fallback string for the NULL case, matching the existing
REMOTE_ADDR guard for consistency.

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