Errors with impossible date

[EgoLaparra]

The parser takes a long to time to parse impossible dates, e.g. "31 April 2018", and then crashes throwing a java.time.DateTimeException.

[bethard]

This is maybe not the most beautiful solution, but putting something like this in the constructor of IntersectionRI at least causes the error to show up nice and early:

  for {
    month <- repeatingIntervals.collectFirst{ case RepeatingField(ChronoField.MONTH_OF_YEAR, month, _, _) => month }
    day <- repeatingIntervals.collectFirst{ case RepeatingField(ChronoField.DAY_OF_MONTH, day, _, _) => day}
  } {
    java.time.MonthDay.of(month.toInt, day.toInt) // throws an exception if this is an invalid combination
  }

I don't know how many other things we might end up special-casing this way, so I'm a little afraid of the precedent, but it's probably worth doing this to avoid searching forever for an impossible time.