message: Fix backwards check on upload buffer being available
diff: @@ -1750,7 +1750,7 @@ bool WrappedID3D12Device::Serialise_MapDataWrite(SerialiserType &ser, ID3D12Reso
  {
  ID3D12Resource *uploadBuf = GetUploadBuffer(cmd.m_CurChunkOffset, rangeSize);
  - if(uploadBuf)
  + if(!uploadBuf)
  {
  RDCERR("Couldn't get upload buffer");
  return false;
  