Control: tags -1 patch
This error correctly notes that subpass is an integer index, not a
pointer, in the underlying API:
https://sources.debian.org/src/vulkan-loader/1.3.296.0-1/vulkan-headers/include/vulkan/vulkan_core.h/?hl=3720#L3703
https://registry.khronos.org/vulkan/specs/latest/man/html/VkGraphicsPipelineCreateInfo.html
Hence, the fix is to use 0 not VK_NULL_HANDLE, as done in gxr-openvr.
https://salsa.debian.org/xrdesktop-team/gxr/-/merge_requests/6
(This code no longer exists upstream, as they have switched this example
to gulkan.)
