bug fix: time_zone used to be a number but now can be a time zone name; guard numberical calculation obsolete code to prevent errors

Author: Pascal Meunier

core/components/com_events/site/controllers/events.php

@@ -1966,7 +1966,11 @@ public function saveTask()
 				$tz = 'Pacific/Kiritimati';
 				break;
 			default:
-				$tz = timezone_name_from_abbr('', $row->time_zone * 3600, -1);
+				// Newer events store an IANA zone name (ex: 'US/Eastern') rather than
+				// a numeric offset, so only convert when we really have a number.
+				$tz = is_numeric($row->time_zone)
+					? timezone_name_from_abbr('', $row->time_zone * 3600, -1)
+					: $row->time_zone;
 		}
 
 		// Publish immediately only for users who can manage publication state