Small AndroidCompatTimeZoneRegistry refactoring

     * @return time zone

     */

    override fun getTimeZone(id: String): TimeZone? {

        // check whether time zone is available on Android

        val tz: TimeZone? = base.getTimeZone(id)

        if (tz == null)     // ical4j doesn't know time zone, return null

            return null

        // check whether time zone is available on Android, too

        val androidTzId =

            try {

                ZoneId.of(id).id

                /* Not available in Android, should return null in a later version.

                   However, we return the ical4j timezone to keep the changes caused by AndroidCompatTimeZoneRegistry introduction

                   as small as possible. */

                return base.getTimeZone(id)

                return tz

            }

        /* Time zone known by Android. Unfortunately, we can't use the Android timezone database directly

           Example: getTimeZone("Europe/Kiev") returns a TimeZone with TZID:Europe/Kyiv since ical4j/3.2.5,

           but most Android devices don't now Europe/Kyiv yet.

           */

        val tz: TimeZone? = base.getTimeZone(id)

        if (tz != null && tz.id != androidTzId) {

        if (tz.id != androidTzId) {

            Ical4Android.log.warning("Using Android TZID $androidTzId instead of ical4j ${tz.id}")

            // create a copy of the VTIMEZONE so that we don't modify the original registry values (which are not immutable)