Some Vulkan types are defined as "non dispatchable handles" and use a
different typedef on 32-bit and 64-bit systems (struct pointer on
64-bit, `uint64_t` otherwise).

https://github.com/KhronosGroup/Vulkan-Headers/blob/0e78ffd1dcfc3e9f14a966b9660dbc59bd967c5c/include/vulkan/vulkan_core.h#L59-L65

Contrarily to `NULL`, `nullptr` can't be converted to `uint64_t` so
build was now failing on 32-bit after converting the codebase from
using `NULL` to `nullptr`.

Fixes #37620.