message: Fix extended thumbnail length not being written
diff: @@ -1676,6 +1676,7 @@ void RenderDoc::FinishCaptureWriting(RDCFile *rdc, uint32_t frameNumber)
  header.width = thumb.width;
  header.height = thumb.height;
  header.format = thumb.format;
  + header.len = (uint32_t)thumb.pixels.size();
  w->Write(header);
  w->Write(thumb.pixels.data(), thumb.pixels.size());
  