Update mgt-agenda.ts (#746)

Fixed `prettyPrintTimeFromDateTime` to not do a UTC->Browser shift on times when a preferred time zone is specified.

Author: jasonjoh

packages/mgt/src/components/mgt-agenda/mgt-agenda.ts

@@ -577,7 +577,15 @@ export class MgtAgenda extends MgtTemplatedComponent {
   }
 
   private prettyPrintTimeFromDateTime(date: Date) {
-    date.setMinutes(date.getMinutes() - date.getTimezoneOffset());
+    // If a preferred time zone was sent in the Graph request
+    // times are already set correctly. Do not adjust
+    if (!this.preferredTimezone) {
+      // If no preferred time zone was specified, the times are in UTC
+      // fall back to old behavior and adjust the times to the browser's
+      // time zone
+      date.setMinutes(date.getMinutes() - date.getTimezoneOffset());
+    }
+
     let hours = date.getHours();
     const minutes = date.getMinutes();
     const ampm = hours >= 12 ? 'PM' : 'AM';