Update lib/src/mobile_scanner.dart

Co-authored-by: Navaron Bracke <brackenavaron@gmail.com>

@@ -302,7 +302,7 @@ class _MobileScannerState extends State<MobileScanner>
   void initState() {
     super.initState();
     controller = widget.controller ?? MobileScannerController();
-    initController();
+    unawaited(initController());
   }
 
   @override