Bug 1738867 - [CalStorageCalendar] Call idleDispatch when clearing the recurring item cache. r=mkmelin

Just in case something is still using it.

Differential Revision: https://phabricator.services.mozilla.com/D130569

--HG--
extra : rebase_source : b326ee22a7be1fe8a7f16505321f5412a1ccfcf5
extra : histedit_source : 255f714d06b11510d9e7f7c88be64ab157213912

calendar/providers/storage/CalStorageCachedItemModel.jsm

@@ -99,6 +99,7 @@ class CalStorageCachedItemModel extends CalStorageItemModel {
       // already waiting and we don't want to break that by throwing away the caches. If it IS
       // complete, we'll continue immediately.
       await this.mRecItemCachePromise;
+      await new Promise(resolve => ChromeUtils.idleDispatch(resolve));
       this.mRecItemCachePromise = null;
     }
     await this.assureRecurringItemCaches();