llama : do not request buffer type if we don't need it anyway Since we use ngl=0 with the Kompute backend to load models on CPU on Linux and Windows, we need to make sure not to call ggml_backend_kompute_buffer_type, which initializes the Vulkan driver. Initializing the Vulkan driver in this case could cause a failure for no good reason (e.g. if it is not available). Also, when we do not create any Kompute buffers, the instance currently does not have an opportunity to be freed until exit-time destructors run, at which point the necessary libraries may have already been unloaded from memory. This causes an observable segfault at exit when loading the model on CPU via the Python bindings.