Obviously erroneous code in JapaneseImperialCalendar::actualMonthLength

[Tagir Valeev]

Hello!

When testing our static analyzer, I've found obviously erroneous code
in java.util.JapaneseImperialCalendar::actualMonthLength

int eraIndex = getTransitionEraIndex(jdate);
if (eraIndex == -1) {
    long transitionFixedDate = sinceFixedDates[eraIndex];
    CalendarDate d = eras[eraIndex].getSinceDate();
    if (transitionFixedDate <= cachedFixedDate) {
       length -= d.getDayOfMonth() - 1;
    } else {
       length = d.getDayOfMonth() - 1;
    }
}

if this 'if' statement is visited then sinceFixedDates[eraIndex] will
surely fail with ArrayIndexOutOfBoundsException. However, judging from
the usages of this method, eraIndex is never -1 here, so the whole
'if' statement is a dead code. I'm not sure whether it should be
removed, or the condition should be changed to 'eraIndex != -1' (and
probably some unit-tests should be written to cover this). I have no
expertise in this code so I'm not sure what would be a proper way to
fix it. Please take a look.

With best regards,
Tagir Valeev.