AP_GPS_MAV: initialise location while handling_msg

This reduces a covarity warning but it likely not really an issue because we always initialise newly allocated memory to zero anyway

libraries/AP_GPS/AP_GPS_MAV.cpp

@@ -59,7 +59,7 @@ void AP_GPS_MAV::handle_msg(mavlink_message_t *msg)
     state.time_week_ms  = packet.time_week_ms;
     state.status = (AP_GPS::GPS_Status)packet.fix_type;
 
-    Location loc;
+    Location loc = {};
     loc.lat = packet.lat;
     loc.lng = packet.lon;
     if (have_alt) {