Fix crash: check availableMetadataObjectTypes before setting QR type

Sources/QRScannerView.swift

@@ -122,7 +122,15 @@ class QRScannerWindowController: NSObject, AVCaptureMetadataOutputObjectsDelegat
         if session.canAddOutput(output) {
             session.addOutput(output)
             output.setMetadataObjectsDelegate(self, queue: .main)
-            output.metadataObjectTypes = [.qr]
+            // 检查摄像头是否支持 QR 码识别
+            if output.availableMetadataObjectTypes.contains(.qr) {
+                output.metadataObjectTypes = [.qr]
+            } else {
+                DispatchQueue.main.async { [weak self] in
+                    self?.showError("Camera does not support QR code scanning")
+                }
+                return
+            }
         }
         
         let previewLayer = AVCaptureVideoPreviewLayer(session: session)