message: Handle vertex shaders with no outputs in GL transfrom feedback
  * We just skip the VS out entirely and make sure we still process any
  geometry/tessellation (which could generate output from no inputs).
diff: @@ -662,6 +662,13 @@ void GLReplay::InitPostVSBuffers(uint32_t eventId)
  GLuint idxBuf = 0;
  + if(vsRefl->outputSignature.empty())
  + {
  + // nothing to do, store an empty cache
  + m_PostVSData[eventId] = GLPostVSData();
  + }
  + else
  + {
  if(!(drawcall->flags & DrawFlags::Indexed))
  {
  uint64_t outputSize = uint64_t(drawcall->numIndices) * stride;
  @@ -1052,6 +1059,7 @@ void GLReplay::InitPostVSBuffers(uint32_t eventId)
  m_PostVSData[eventId].vsout.hasPosOut = hasPosition;
  m_PostVSData[eventId].vsout.topo = drawcall->topology;
  + }
  if(tesRefl || gsRefl)
  {
  @@ -1596,6 +1604,8 @@ void GLReplay::InitPostVSBuffers(uint32_t eventId)
  rdcarray<GLPostVSData::InstData> instData;
  + GLuint primsWritten = 0;
  +
  if((drawcall->flags & DrawFlags::Instanced) && drawcall->numInstances > 1)
  {
  uint64_t prevVertCount = 0;
  @@ -1620,7 +1630,7 @@ void GLReplay::InitPostVSBuffers(uint32_t eventId)
  drv.glGetQueryObjectuiv(DebugData.feedbackQueries[0], eGL_QUERY_RESULT, &primsWritten);
  }
  - error = false;
  + bool error = false;
  if(primsWritten == 0)
  {
  @@ -1629,7 +1639,7 @@ void GLReplay::InitPostVSBuffers(uint32_t eventId)
  }
  // get buffer data from buffer attached to feedback object
  - data = (float *)drv.glMapNamedBufferEXT(DebugData.feedbackBuffer, eGL_READ_ONLY);
  + float *data = (float *)drv.glMapNamedBufferEXT(DebugData.feedbackBuffer, eGL_READ_ONLY);
  if(data == NULL)
  {
  @@ -1695,14 +1705,14 @@ void GLReplay::InitPostVSBuffers(uint32_t eventId)
  drv.glNamedBufferDataEXT(lastoutBuffer, stride * m_PostVSData[eventId].gsout.numVerts, data,
  eGL_STATIC_DRAW);
  - byteData = (byte *)data;
  + byte *byteData = (byte *)data;
  - nearp = 0.1f;
  - farp = 100.0f;
  + float nearp = 0.1f;
  + float farp = 100.0f;
  - pos0 = (Vec4f *)byteData;
  + Vec4f *pos0 = (Vec4f *)byteData;
  - found = false;
  + bool found = false;
  for(uint32_t i = 1; hasPosition && i < m_PostVSData[eventId].gsout.numVerts; i++)
  {
  