Bug 1921658 - Set CalendarBaseView.weekStartOffset after the default preferences. r=aleca

In the earliest case, `ensureInitialized` runs as tabs are restored, so always after
`setLocaleDefaultPreferences`. Unlike `connectedCallback` which runs as soon as the custom element
is defined and attached to the DOM.

It needs to happen after `setLocaleDefaultPreferences` to get the correct value if the correct
value is not 0.

Differential Revision: https://phabricator.services.mozilla.com/D226086

--HG--
extra : amend_source : 493e0709b2f62a375c56ab3e31a69932401bd1c1

calendar/base/content/calendar-base-view.js

@@ -87,7 +87,6 @@
       });
 
       this.mSelectedItems = [];
-      this.weekStartOffset = Services.prefs.getIntPref("calendar.week.start");
     }
 
     ensureInitialized() {
@@ -96,6 +95,7 @@
       }
       this.#isInitialized = true;
 
+      this.weekStartOffset = Services.prefs.getIntPref("calendar.week.start");
       this.calICalendarView = this.getCustomInterfaceCallback(Ci.calICalendarView);
 
       this.addEventListener("move", event => {