fix bug with null scan window; abort if texture is null

@@ -269,7 +269,7 @@ class MobileScannerHandler(
     }
 
     private fun updateScanWindow(call: MethodCall, result: MethodChannel.Result) {
-        mobileScanner!!.scanWindow = call.argument<List<Float>?>("rect")
+        mobileScanner?.scanWindow = call.argument<List<Float>?>("rect")
 
         result.success(null)
     }

@@ -287,9 +287,19 @@ class MethodChannelMobileScanner extends MobileScannerPlatform {
 
   @override
   Future<void> updateScanWindow(Rect? window) async {
+    if (_textureId == null) {
+      return;
+    }
+
+    List<double>? points;
+
+    if (window != null) {
+      points = [window.left, window.top, window.right, window.bottom];
+    }
+
     await methodChannel.invokeMethod<void>(
       'updateScanWindow',
-      {'rect': window},
+      {'rect': points},
     );
   }
 

@@ -288,6 +288,13 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
     await MobileScannerPlatform.instance.setTorchState(newState);
   }
 
+  /// Update the scan window with the given [window] rectangle.
+  ///
+  /// If [window] is null, the scan window will be reset to the full camera preview.
+  Future<void> updateScanWindow(Rect? window) async {
+    await MobileScannerPlatform.instance.updateScanWindow(window);
+  }
+
   @override
   Future<void> dispose() async {
     if (_isDisposed) {