Eliminating some QML errors when the application is shutting down.

src/FlightMap/MapItems/VehicleMapItem.qml

@@ -39,7 +39,7 @@ MapQuickItem {
 
     anchorPoint.x:  vehicleIcon.width  / 2
     anchorPoint.y:  vehicleIcon.height / 2
-    visible:        vehicle.coordinateValid
+    visible:        vehicle && vehicle.coordinateValid
 
     sourceItem: Image {
         id:         vehicleIcon
@@ -51,7 +51,7 @@ MapQuickItem {
         transform: Rotation {
             origin.x:   vehicleIcon.width  / 2
             origin.y:   vehicleIcon.height / 2
-            angle:      vehicle.heading
+            angle:      vehicle ? vehicle.heading : 0
         }
     }
 }

src/ui/toolbar/MainToolBarIndicators.qml

@@ -58,10 +58,12 @@ Row {
                 return colorOrange;
             if (activeVehicle.messageTypeError)
                 return colorRed;
+            // Cannot be so make make it obnoxious to show error
+            console.log("Invalid vehicle message type")
+            return "purple";
         }
-        // Cannot be so make make it obnoxious to show error
-        console.log("Invalid vehicle message type")
-        return "purple";
+        //-- It can only get here when closing (vehicle gone while window active)
+        return "white";
     }
 
     function getBatteryVoltageText() {