Commit c3fd455 changed LibTimeZone to fall back to the system time zone
when we fail to parse the TZ environment variable. This behavior differs
from both our LibC and glibc; they abort parsing and default to UTC.
This changes LibTimeZone to behave the same way to avoid a very awkward
situation where some parts of the codebase thinks the timezone is UTC,
and others think the timezone is whatever /etc/timezone indicates.
ed612d835d