Return vkGetInstanceProcAddr from Hook_vkGetInstanceProcAddr for use by other plugins

[chris-unity]

Currently our example code returns NULL, which would prevent other plugins from initialising.

This PR updates the code to be compatible with the V2 API use case.

[Darkgrouptw]

Thank you bro.

I build my native plugin on android and it crash. And solve it by this command.

You save my day!

[MoMoPF]

Great! It solved my crash problem when I intercept vkCreateInstance! Thanks!