Skip custom instrument widget test if none exists.

src/FlightDisplay/FlightDisplayViewMap.qml

@@ -101,7 +101,7 @@ FlightMap {
         var vehiclePoint = flightMap.fromCoordinate(_activeVehicleCoordinate, false /* clipToViewport */)
         var toolStripRightEdge = mapFromItem(toolStrip, toolStrip.x, 0).x + toolStrip.width
         var instrumentsWidth = 0
-        if (QGroundControl.corePlugin.options.instrumentWidget.widgetPosition === CustomInstrumentWidget.POS_TOP_RIGHT) {
+        if (QGroundControl.corePlugin.options.instrumentWidget && QGroundControl.corePlugin.options.instrumentWidget.widgetPosition === CustomInstrumentWidget.POS_TOP_RIGHT) {
             // Assume standard instruments
             instrumentsWidth = flightDisplayViewWidgets.getPreferredInstrumentWidth()
         }