Panic with TZ="pBB24"

[pitdicker]

Gave my first try fuzzing chrono, starting with setting the TZ env variable.
It came up with "pBB24"

We accept an offset of +24 hours for a time zone named "pBB".
But in chrono we define that an offset can be at most 23:59:59, and return LocalResult::None (and then panic) when trying to do anything with Local.

[pitdicker]

The fix is to change a 24 to 23 in tz_info::rule::parse_offset.