Bug 1558522 - Ensure that file actors created after the database was closed are expired. r=asuth

Differential Revision: https://phabricator.services.mozilla.com/D48046

--HG--
extra : moz-landing-system : lando

dom/indexedDB/IDBDatabase.cpp

@@ -1081,6 +1081,8 @@ void IDBDatabase::LastRelease() {
 
   CloseInternal();
 
+  ExpireFileActors(/* aExpireAll */ true);
+
   if (mBackgroundActor) {
     mBackgroundActor->SendDeleteMeInternal();
     MOZ_ASSERT(!mBackgroundActor, "SendDeleteMeInternal should have cleared!");