Save timezone to current timezone if no timezone is set

The preferences showed the detected timezone as the selected timezone if no timezone was null. Now we force set it in that case.

Closes #815

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

js/src/views/Settings/Preferences.vue

@@ -144,7 +144,11 @@ export default class Preferences extends Vue {
     if (this.loggedUser?.settings?.timezone) {
       return this.loggedUser.settings.timezone;
     }
-    return Intl.DateTimeFormat().resolvedOptions().timeZone;
+    const detectedTimezone = Intl.DateTimeFormat().resolvedOptions().timeZone;
+    if (this.loggedUser?.settings?.timezone === null) {
+      this.updateUserSettings({ timezone: detectedTimezone });
+    }
+    return detectedTimezone;
   }
 
   set selectedTimezone(selectedTimezone: string) {