fix missing isClosed checks

@@ -119,9 +119,11 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
   void _setupListeners() {
     _barcodesSubscription = MobileScannerPlatform.instance.barcodesStream
         .listen((BarcodeCapture? barcode) {
-      if (!_barcodesController.isClosed && barcode != null) {
-        _barcodesController.add(barcode);
+      if (_barcodesController.isClosed || barcode == null) {
+        return;
       }
+
+      _barcodesController.add(barcode);
     });
 
     _torchStateSubscription = MobileScannerPlatform.instance.torchStateStream

@@ -113,7 +113,9 @@ class MobileScannerWeb extends MobileScannerPlatform {
 
     try {
       // Clear the existing barcodes.
-      _barcodesController.add(const BarcodeCapture());
+      if (!_barcodesController.isClosed) {
+        _barcodesController.add(const BarcodeCapture());
+      }
 
       // Listen for changes to the media track settings.
       _barcodeReader.setMediaTrackSettingsListener(

@@ -187,13 +187,15 @@ final class ZXingBarcodeReader extends BarcodeReader {
         _reader as JSAny?,
         _reader?.videoElement as JSAny?,
         (Result? result, JSAny? error) {
-          if (!controller.isClosed && result != null) {
-            controller.add(
-              BarcodeCapture(
-                barcodes: [result.toBarcode],
-              ),
-            );
+          if (controller.isClosed || result == null) {
+            return;
           }
+
+          controller.add(
+            BarcodeCapture(
+              barcodes: [result.toBarcode],
+            ),
+          );
         }.toJS,
       );
     };