message: Fix layout transitions in renderheadless
  Old code had an UNDEFINED to TRANSFER_SRC_OPTIMAL transitions
  causing the read-back image to also be undefined.
diff: @@ -415,7 +415,7 @@ public:
  attchmentDescriptions[0].stencilLoadOp = VK_ATTACHMENT_LOAD_OP_DONT_CARE;
  attchmentDescriptions[0].stencilStoreOp = VK_ATTACHMENT_STORE_OP_DONT_CARE;
  attchmentDescriptions[0].initialLayout = VK_IMAGE_LAYOUT_UNDEFINED;
  - attchmentDescriptions[0].finalLayout = VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL;
  + attchmentDescriptions[0].finalLayout = VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL;
  // Depth attachment
  attchmentDescriptions[1].format = depthFormat;
  attchmentDescriptions[1].samples = VK_SAMPLE_COUNT_1_BIT;
  @@ -706,17 +706,7 @@ public:
  VK_PIPELINE_STAGE_TRANSFER_BIT,
  VkImageSubresourceRange{ VK_IMAGE_ASPECT_COLOR_BIT, 0, 1, 0, 1 });
  - // Transition color attachment to transfer source
  - vks::tools::insertImageMemoryBarrier(
  - copyCmd,
  - colorAttachment.image,
  - 0,
  - VK_ACCESS_TRANSFER_READ_BIT,
  - VK_IMAGE_LAYOUT_UNDEFINED,
  - VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL,
  - VK_PIPELINE_STAGE_TRANSFER_BIT,
  - VK_PIPELINE_STAGE_TRANSFER_BIT,
  - VkImageSubresourceRange{ VK_IMAGE_ASPECT_COLOR_BIT, 0, 1, 0, 1 });
  + // colorAttachment.image is already in VK_IMAGE_LAYOUT_TRANSFER_SRC_OPTIMAL, and does not need to be transitioned
  VkImageCopy imageCopyRegion{};
  imageCopyRegion.srcSubresource.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
  