This is another attempt to fix 1437668.  The assertion here should
be safe, since the rules of networkstatus_get_param() keep the value
it returns in range.

Bugfix on dcee4d4c, bug not in any
released Tor.

Another way to try to prevent a recurrence of 26485.

Prevents bug 26485; bugfix on 0.1.1.6-alpha.