vk::DispatchLoaderDynamic::init(vk::VkInstance) overwrites vkGetInstanceProcAddr with NULL

[dneto0]

The vk::DispatchLoaderDynamic::init(vk::VkInstance) method uses vkGetInstanceProcAddr to overwrite vkGetInstanceProcAddr itself.

See https://github.com/KhronosGroup/Vulkan-Headers/blob/d594f70127b4198286b3472a48bee56e341259cd/include/vulkan/vulkan.hpp#L11864

      vkGetInstanceProcAddr = PFN_vkGetInstanceProcAddr( vkGetInstanceProcAddr( instance, "vkGetInstanceProcAddr" ) );

But the value is NULL, because a valid 'instance' is provided and so it falls into the last row in the table in 4.1 "Command Function Pointers" https://www.khronos.org/registry/vulkan/specs/1.2-extensions/html/vkspec.html#initialization-functionpointers

But then that causes a crash in the very next function pointer initialization call.

This bad behaviour was uncovered by a recent fix in the loader: KhronosGroup/Vulkan-Loader#692

[asuessenbach]

That was really tricky to get from the spec!
Thanks for providing a fix for this issue.