pfctl: fix crash on "pfctl -a '*' -vvsr"

When printing a nat anchor we don't have rule information, or rule
counters. Do not attempt to print them. The information is nonsensical
anyway, and this can cause a crash converting the timestamp to a string,
as years in the very distant future use more digits, and we exceed the
30 byte buffer allocated for this.

MFC after: 2 weeks
Sponsored by: Orange Business Services