message: Vulkan: fix bad depth clears.
  The Vulkan backend was failing to clear the depth buffer in apps that do
  not have a textured skybox, such as hellotriangle.
diff: @@ -208,7 +208,7 @@ VulkanAttachment VulkanRenderTarget::getColor() const {
  }
  VulkanAttachment VulkanRenderTarget::getDepth() const {
  - return mOffscreen ? mDepth : VulkanAttachment {};
  + return mOffscreen ? mDepth : mContext.currentSurface->depth;
  }
  VulkanVertexBuffer::VulkanVertexBuffer(VulkanContext& context, VulkanStagePool& stagePool,
  