Fix validation of VAAPI/QSV render node path (#13786)

Signed-off-by: nyanmisaka <nst799610810@gmail.com>

MediaBrowser.Controller/MediaEncoding/EncodingHelper.cs

@@ -862,9 +862,9 @@ namespace MediaBrowser.Controller.MediaEncoding
                 && _mediaEncoder.EncoderVersion >= _minFFmpegVaapiDeviceVendorId;
 
             // Priority: 'renderNodePath' > 'vendorId' > 'kernelDriver'
-            var driverOpts = string.IsNullOrEmpty(renderNodePath)
-                ? (haveVendorId ? $",vendor_id={vendorId}" : (string.IsNullOrEmpty(kernelDriver) ? string.Empty : $",kernel_driver={kernelDriver}"))
-                : renderNodePath;
+            var driverOpts = File.Exists(renderNodePath)
+                ? renderNodePath
+                : (haveVendorId ? $",vendor_id={vendorId}" : (string.IsNullOrEmpty(kernelDriver) ? string.Empty : $",kernel_driver={kernelDriver}"));
 
             // 'driver' behaves similarly to env LIBVA_DRIVER_NAME
             driverOpts += string.IsNullOrEmpty(driver) ? string.Empty : ",driver=" + driver;