improve portmap logging

src/alert.cpp

@@ -1146,7 +1146,7 @@ namespace {
 
 	std::string portmap_log_alert::message() const
 	{
-		char ret[600];
+		char ret[1024];
 		std::snprintf(ret, sizeof(ret), "%s: %s"
 			, nat_type_str[static_cast<int>(map_transport)]
 			, log_message());

src/natpmp.cpp

@@ -285,7 +285,9 @@ void natpmp::mapping_log(char const* op, mapping_t const& m) const
 			, m.external_port
 			, m.local_port
 			, to_string(m.act)
-			, total_seconds(m.expires - aux::time_now()));
+			, (m.expires.time_since_epoch() != seconds(0))
+				? total_seconds(m.expires - aux::time_now())
+				: std::int64_t(0));
 	}
 }