FAB-302: fix panic for block-listener

when receive a rejection event with no "-listen-to-rejections",
adapter of block-listener push a nil to notfy channel. This will
cause nil pointer panic. Fix the handle logic.

Change-Id: I8391af03acf32c6d99d613db6e2e7dc13d2424cc
Signed-off-by: jiangyaoguo <jiangyaoguo@gmail.com>

examples/events/block-listener/block-listener.go

@@ -57,16 +57,17 @@ func (a *adapter) Recv(msg *pb.Event) (bool, error) {
 		a.notfy <- o
 		return true, nil
 	}
-	if o, e := msg.Event.(*pb.Event_Rejection); e && a.listenToRejections {
-		a.rejected <- o
+	if o, e := msg.Event.(*pb.Event_Rejection); e {
+		if a.listenToRejections {
+			a.rejected <- o
+		}
 		return true, nil
 	}
 	if o, e := msg.Event.(*pb.Event_ChaincodeEvent); e {
 		a.cEvent <- o
 		return true, nil
 	}
-	a.notfy <- nil
-	return false, nil
+	return false, fmt.Errorf("Receive unkown type event: %v", msg)
 }
 
 //Disconnected implements consumer.EventAdapter interface for disconnecting