message: Metal: fix bad upload size in blitDepthPlane.
  This was caught by ASAN.
diff: @@ -390,7 +390,7 @@ void MetalBlitter::blitDepthPlane(id<MTLCommandBuffer> cmdBuffer, bool blitColor
  .srcOffset = { sourceRegion.origin.x, sourceRegion.origin.y }
  };
  - [encoder setVertexBytes:vertices length:(sizeof(math::float4) * 3) atIndex:0];
  + [encoder setVertexBytes:vertices length:(sizeof(math::float2) * 3) atIndex:0];
  [encoder setFragmentBytes:&fargs length:sizeof(FragmentArgs) atIndex:0];
  [encoder drawPrimitives:MTLPrimitiveTypeTriangle vertexStart:0 vertexCount:3];
  [encoder endEncoding];
  