Function hgdirectffi::rustlazyancestors_next

#[no_mangle]
pub extern "C" fn rustlazyancestors_next(
    raw: *mut AncestorsIterator<Index>
) -> c_long

Iteration main method to be called from C code

We convert the end of iteration into NULL_REVISION, it will be up to the C wrapper to convert that back into a Python end of iteration