ZP-1285 Missed other instance of timezone lookup in Recurrence -- fixed.

Note: Needs more eyeballs; this appears correct but the original code goes
back a *long* way, and until recently I had not noted problems with time
zone conversion.  Why it failed now, but not before, is not clear.

Released under the Affero GNU General Public License (AGPL) version 3.

src/backend/caldav/caldav.php

@@ -557,7 +557,7 @@ class BackendCalDAV extends BackendDiff {
             if (count($rec) > 0) {
                 $recurrence_id = reset($rec);
                 $exception = new SyncAppointmentException();
-                $tzid = TimezoneUtil::ParseTimezone($recurrence_id->GetParameterValue("TZID"));
+                $tzid = TimezoneUtil::GetPhpSupportedTimezone($recurrence_id->GetParameterValue("TZID"));
                 if (!$tzid) {
                     $tzid = $timezone;
                 }