Added try catch with errorhandling

lib/widgets/scanner.dart

@@ -37,12 +37,28 @@ 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) {
-    final List<Barcode> barcodes = capture.barcodes;
-    for (final barcode in barcodes) {
-      if (barcode.rawValue != null) {
-        return handleSucces(barcode.rawValue);
+    try {
+      final List<Barcode> barcodes = capture.barcodes;
+      for (final barcode in barcodes) {
+        if (barcode.rawValue != null) {
+          return handleSucces(barcode.rawValue);
+        }
       }
+    } catch (e) {
+      handleError();
     }
   }