def zeropad(splitver, idx, padlen):
    """
    Zero-pad an element of an OS/radio version to a certain length.

    :param splitver: OS/radio version, but split into quarters.
    :type splitver: list(str)

    :param idx: Index of splitver which must be checked.
    :type idx: int

    :param padlen: Length to pad to.
    :type padlen: int
    """
    if len(splitver[idx]) < padlen:
        splitver[idx] = splitver[idx].rjust(padlen, "0")
    return splitver