listerInformer can block calls to drain and multiListerWatcher

The listerInformer's sendEvent can be blocked by the multiListerWatcher when it is already processing another event. As the sendEvent function holds the listerInformer's lock this can in turn block calls to drain which can in turn block the event processing loop

• sendEvent blocks drain
• drain blocks event processing loop
• event processing loop blocks sendEvent

The result is that event processing for that instance of the multiListerWatcher will cease for all namespaces.