Bug 1286798 - Part 24: A new exclusive directory lock shouldn't invalidate existing internal directory locks; r=asuth

This fixes an intermittent failure when multiple clearStoragesForPrincipal() are called at the same time.

dom/quota/ActorsParent.cpp

@@ -5262,9 +5262,9 @@ QuotaManager::OpenDirectoryInternal(const Nullable<PersistenceType>& aPersistenc
     lock->GetBlockedOnLocks();
 
   for (DirectoryLockImpl* blockedOnLock : blockedOnLocks) {
-    blockedOnLock->Invalidate();
-
     if (!blockedOnLock->IsInternal()) {
+      blockedOnLock->Invalidate();
+
       MOZ_ASSERT(!blockedOnLock->GetClientType().IsNull());
       Client::Type clientType = blockedOnLock->GetClientType().Value();
       MOZ_ASSERT(clientType < Client::TypeMax());