message: Add assert that command buffer is non-NULL
diff: @@ -365,6 +365,7 @@ int StageIndex(VkShaderStageFlagBits stageFlag)
  void DoPipelineBarrier(VkCommandBuffer cmd, uint32_t count, VkImageMemoryBarrier *barriers)
  {
  + RDCASSERT(cmd != VK_NULL_HANDLE);
  ObjDisp(cmd)->CmdPipelineBarrier(Unwrap(cmd), VK_PIPELINE_STAGE_ALL_COMMANDS_BIT,
  VK_PIPELINE_STAGE_ALL_COMMANDS_BIT, 0, 0,
  NULL, // global memory barriers
  @@ -374,6 +375,7 @@ void DoPipelineBarrier(VkCommandBuffer cmd, uint32_t count, VkImageMemoryBarrier
  void DoPipelineBarrier(VkCommandBuffer cmd, uint32_t count, VkBufferMemoryBarrier *barriers)
  {
  + RDCASSERT(cmd != VK_NULL_HANDLE);
  ObjDisp(cmd)->CmdPipelineBarrier(Unwrap(cmd), VK_PIPELINE_STAGE_ALL_COMMANDS_BIT,
  VK_PIPELINE_STAGE_ALL_COMMANDS_BIT, 0, 0,
  NULL, // global memory barriers
  @@ -383,6 +385,7 @@ void DoPipelineBarrier(VkCommandBuffer cmd, uint32_t count, VkBufferMemoryBarrie
  void DoPipelineBarrier(VkCommandBuffer cmd, uint32_t count, VkMemoryBarrier *barriers)
  {
  + RDCASSERT(cmd != VK_NULL_HANDLE);
  ObjDisp(cmd)->CmdPipelineBarrier(Unwrap(cmd), VK_PIPELINE_STAGE_ALL_COMMANDS_BIT,
  VK_PIPELINE_STAGE_ALL_COMMANDS_BIT, 0, count,
  barriers, // global memory barriers
  