Attempting to fix AIAircraft/controller crash

Add an assertion that controller has been cleared before the AIAircraft
destructor is run. If it’s not, then we are too late, don’t try to
sign off since the controller is probably gone.

Sentry-Id: FLIGHTGEAR-15

src/AIModel/AIAircraft.cxx

@@ -115,9 +115,15 @@ FGAIAircraft::FGAIAircraft(FGAISchedule* ref) : /* HOT must be disabled for AI A
 }
 
 
-FGAIAircraft::~FGAIAircraft() {
+FGAIAircraft::~FGAIAircraft()
-    if (controller)
+{
-        controller->signOff(getID());
+    assert(!controller);
+    if (controller) {
+        // we no longer signOff from controller here, controller should
+        // have been cleared using clearATCCOntrollers
+        // see FLIGHTGEAR-15 on Sentry
+        SG_LOG(SG_AI, SG_ALERT, "Destruction of AIAircraft which was not unbound");
+    }
 }
 
 
@@ -419,6 +425,10 @@ double FGAIAircraft::calcVerticalSpeed(double vert_ft, double dist_m, double spe
 
 void FGAIAircraft::clearATCController()
 {
+    if (controller) {
+        controller->signOff(getID());
+    }
+
     controller = 0;
     prevController = 0;
     towerController = 0;

src/ATC/trafficcontrol.cxx

@@ -561,8 +561,10 @@ FGATCController::FGATCController()
 
 FGATCController::~FGATCController()
 {
-    auto mgr = globals->get_subsystem<FGATCManager>();
+    if (initialized) {
-    mgr->removeController(this);
+        auto mgr = globals->get_subsystem<FGATCManager>();
+        mgr->removeController(this);
+    }
 }
 
 void FGATCController::init()