Sekiro under Proton crashes with thunks
Sekiro when running under Proton crashes if thunks are enabled. For some reason it gets a nullptr dereference in vkCreateInstance because the pointer is null.

With a hack I can get it to work:
```diff
diff --git a/ThunkLibs/libvulkan/Host.cpp b/ThunkLibs/libvulkan/Host.cpp
index 1cfaa4227..de5cf2ec9 100644
--- a/ThunkLibs/libvulkan/Host.cpp
+++ b/ThunkLibs/libvulkan/Host.cpp
@@ -77,6 +77,10 @@ static VkResult FEXFN_IMPL(vkCreateInstance)(const VkInstanceCreateInfo* a_0, co
     }
   }

+  if (LDR_PTR(vkCreateInstance) == nullptr) [[unlikely]] {
+    (void*&)LDR_PTR(vkCreateInstance) = (void*)dlsym_default(fexldr_ptr_libvulkan_so, "vkCreateInstance");
+  }
+
   VkInstance out;
   auto ret = LDR_PTR(vkCreateInstance)(vk_struct_base, nullptr, &out);
   if (ret == VK_SUCCESS) {
   ```

Weirdly, the other symbols loaded with `DoSetupWithInstance` are populated
```
(gdb) p/x fexldr_ptr_libvulkan_vkCreateInstance
$1 = 0x0
(gdb) p/x fexldr_ptr_libvulkan_vkCreateDevice
$2 = 0x7fffc6f9f990
(gdb) p/x fexldr_ptr_libvulkan_vkGetDeviceProcAddr
$3 = 0x7fffc6f9e1a0
```

This should be investigated, I'm not sure how many games are hitting this issue.