Copter: reload takeoff cmd on arm when using AllowTakeOffWithoutRaisi…

…ngThrottle

USING AUTO_OPTIONS 135 we set auto mode and arm from it if we got a takeoff cmd as first nav cmd.
Doing this, the takeoff cmd is loaded when we enter the auto mode and set the target alt relatively to origin https://github.com/ArduPilot/ardupilot/blob/master/ArduCopter/mode_auto.cpp#L343
This is never called again. So when we reset the home from the first arming, we don't update the target alt relativly to origin. This leads to a wrong takeoff alt settle due to the alt drift on ground.

ArduCopter/mode_auto.cpp

@@ -992,7 +992,10 @@ void ModeAuto::takeoff_run()
     // if the user doesn't want to raise the throttle we can set it automatically
     // note that this can defeat the disarm check on takeoff
     if ((copter.g2.auto_options & (int32_t)Options::AllowTakeOffWithoutRaisingThrottle) != 0) {
-        copter.set_auto_armed(true);
+        if (motors->armed() && copter.ap.auto_armed == false) {
+            copter.mode_auto.mission.restart_current_nav_cmd();  // reload the takeoff command after arming home update
+            copter.set_auto_armed(true);
+        }
     }
     auto_takeoff.run();
 }