message: Fix potential Metal memory leak
diff: @@ -78,9 +78,6 @@ bool MetalExternalImage::isValid() const noexcept {
  }
  void MetalExternalImage::set(CVPixelBufferRef image) noexcept {
  - // This pool is necessary because set is called outside of a frame.
  - NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
  -
  CVPixelBufferRelease(mImage);
  CVBufferRelease(mTexture);
  [mRgbTexture release];
  @@ -93,6 +90,9 @@ void MetalExternalImage::set(CVPixelBufferRef image) noexcept {
  return;
  }
  + // This pool is necessary because set is called outside of a frame.
  + NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
  +
  OSType formatType = CVPixelBufferGetPixelFormatType(image);
  ASSERT_POSTCONDITION(formatType == kCVPixelFormatType_32BGRA ||
  formatType == kCVPixelFormatType_420YpCbCr8BiPlanarFullRange,
  