properly handle takeoff waypoint when not currently at takeoff location

src/modules/navigator/mission.h

@@ -185,6 +185,7 @@ private:
 	int _current_offboard_mission_index;
 	bool _need_takeoff;					/**< if true, then takeoff must be performed before going to the first waypoint (if needed) */
 	bool _takeoff;						/**< takeoff state flag */
+	bool _takeoff_finished;					/**< set if takeoff was requested before and is now done */
 
 	enum {
 		MISSION_TYPE_NONE,