Existing outfiles (check_outfile_overwrite = False) is handled inconsistently

[stefan-apollo]

In rib_builder:

    if not check_outfile_overwrite(out_file, force):
        if dist_info is not None and dist_info.global_size > 1:
            dist_info.local_comm.Abort()  # stop this and other processes
        raise FileExistsError(f"Output file {out_file} already exists")

In ablations:

        if not check_outfile_overwrite(out_file, force):
            raise FileExistsError("Not overwriting output file")

In plotting:

    if not check_outfile_overwrite(out_file, force):
        return None