Fix timezone issue by providing default 'UTC' value

Co-authored-by: estruyf <2900833+estruyf@users.noreply.github.com>

src/helpers/PanelSettings.ts

@@ -70,7 +70,7 @@ export class PanelSettings {
         },
         date: {
           format: Settings.get<string>(SETTING_DATE_FORMAT) || '',
-          timezone: Settings.get<string>(SETTING_GLOBAL_TIMEZONE) || ''
+          timezone: Settings.get<string>(SETTING_GLOBAL_TIMEZONE) || 'UTC'
         },
         tags: (await TaxonomyHelper.get(TaxonomyType.Tag)) || [],
         categories: (await TaxonomyHelper.get(TaxonomyType.Category)) || [],

src/utils/formatInTimezone.ts

@@ -2,6 +2,6 @@ import { SETTING_GLOBAL_TIMEZONE } from '../constants';
 import { DateHelper, Settings } from '../helpers';
 
 export const formatInTimezone = (date: Date, dateFormat: string) => {
-  const timezone = Settings.get<string>(SETTING_GLOBAL_TIMEZONE);
+  const timezone = Settings.get<string>(SETTING_GLOBAL_TIMEZONE) || 'UTC';
   return DateHelper.formatInTimezone(date, dateFormat, timezone) || '';
 };