vk: Only finish wayland wsi if we created it
vk: Only finish wayland wsi if we created it

Failure during instance creation will leave instance->wayland_wsi
undefined. When we then try to clean that up we crash. Set
instance->wayland_wsi to NULL on failure and only clean it up if it's
non-NULL.

Fixes part of dEQP-VK.api.object_management.alloc_callback_fail.*

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler