Potential null pointer dereference with `Deref` implementation on `Buf`

We consider that there should be a null check before dereference on `Buf`. https://github.com/rust-lang/git2-rs/blob/03ec58122907ba45fc9f9ba7721a7e62be1f719e/src/buf.rs#L23-L49 In this code, if we dereference the buffer right after calling `new()`, it pass null pointer to the unsafe function `slice::from_raw_parts`. Based on the documentation of function, > data must be non-null and aligned even for zero-length slices or slices of ZSTs. Even though it is zero-length slice, we should ensure that the pointer is not null. How do you think about it?