QuotaManager: Don't fire callback if it's null

BUG=n/a
R=nhiroki@chromium.org

Review URL: https://codereview.chromium.org/147143005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247879 0039d316-1c4b-4281-b951-d872f2087c98

webkit/browser/quota/quota_manager.cc

@@ -987,7 +987,7 @@ void QuotaManager::SetTemporaryGlobalOverrideQuota(
   }
 
   if (db_disabled_) {
-    if (callback.is_null())
+    if (!callback.is_null())
       callback.Run(kQuotaErrorInvalidAccess, -1);
     return;
   }