8148570: TzdbZoneRulesCompiler.java throws Null Pointer Exception While Compiling and building TZDB data file Summary: While getting value from DayOfWeek, -1 is returned if the DayOfWeek is null. The reason to return “-1” being, the same value is checked later while getting day-of-week byte (dowbyte) at line no. 251, ZoneRules.java. Reviewed-by: rriggs, aefimov