Multiple closes on the same result channle in MemoryQueueFactory #150

func (f *MemoryQueueFactory) NewSourceTube(ctx context.Context, configMap ConfigMap) (<-chan Record, error) {  
	config := NewSourceQueueConfig(configMap)  
	result := make(chan Record)  
	var wg sync.WaitGroup  
	for _, topic := range config.Topics {  
		wg.Add(1)   
		t := topic  
		go func() {  
			<-ctx.Done()      
			f.release(t)      
		}()  
  
		go func() {  
			defer wg.Done()   
			c := f.getOrCreateChan(t)  
			for {  
				select {  
				case <-ctx.Done():  
					return   
				case event := <-c:  
					result <- event   
				}  
			}  
		}()  
	}  
  
	go func() {  
		wg.Wait() 
		close(result) 
	}()  
  
	return result, nil  
}