reverseName on 0.0.0.0/0 returns invalid name

The name returned by IP when using top level address 0.0.0.0/0 returned a leading dot, which is an invalid domain name:

In [3]: IP('0.0.0.0/0').reverseName()
Out[3]: '.in-addr.arpa.'

The correct response should be in-addr.arpa.

on line 921 this could be changed to:

return "%s%s.in-addr.arpa." % (nibblepart, s) if nibbblepart else "in-addr.arpa."

Thanks