RTL_mission_reverse: start from previous WP if RTL is triggered while in Mission

Signed-off-by: Silvan Fuhrer <silvan@auterion.com>

src/modules/navigator/rtl_mission_fast_reverse.h

@@ -57,6 +57,7 @@ public:
 
 	void on_activation() override;
 	void on_active() override;
+	void on_inactive() override;
 
 	rtl_time_estimate_s calc_rtl_time_estimate() override;
 
@@ -65,5 +66,7 @@ private:
 	void setActiveMissionItems() override;
 	void handleLanding(WorkItemType &new_work_item_type);
 
+	int _mission_index_prior_rtl{-1};
+
 	uORB::SubscriptionData<home_position_s> _home_pos_sub{ORB_ID(home_position)};		/**< home position subscription */
 };