Do not throw IndexOutOfBoundsException when no task configuration is available

It's possible for a connector implementation to return an empty list of task configurations under certain conditions that cause the logic within the #taskConfigs(int) method to return an empty list of task configurations. This creates an issue in the embedded engine as it assumes that the returned collection is non-null and contains at most 1 element in the collection. We should make the embedded engine more resilient such that if the connector returns an empty task configuration collection that the embedded engine reports that it can't start the connector's task and ends. This should then avoid the case where the connector couldn't be started (see IndexOutOfBoundsException here.