Added try catch with errorhandling

lib/widgets/scanner.dart

@@ -37,13 +37,29 @@ class MyScannerState extends State<MyScanner> {
     });
   }
 
+  void handleError() {
+    setState(() {
+      scanning = false;
+      AwesomeDialog(
+        context: context,
+        dialogType: DialogType.error,
+        title: 'Fehler',
+        desc: 'Der QR-Code war fehlerhaft!',
+      ).show();
+    });
+  }
+
   void onDetect(capture) {
+    try {
       final List<Barcode> barcodes = capture.barcodes;
       for (final barcode in barcodes) {
         if (barcode.rawValue != null) {
           return handleSucces(barcode.rawValue);
         }
       }
+    } catch (e) {
+      handleError();
+    }
   }
 
   @override