fix the set of events received by ChildrenW

In accordance with
https://github.com/apache/zookeeper/blob/c74658d398cdc1d207aa296cb6e20de00faec03e/zookeeper-client/zookeeper-client-c/src/zk_hashtable.c#L297-L314
ChildrenW should not receive data change events of the observed node.

conn.go

@@ -801,7 +801,7 @@ func (c *Conn) recvLoop(conn net.Conn) error {
 
  if res.Xid == -1 {
  res := &watcherEvent{}
- _, err := decodePacket(buf[16:blen], res)
+ _, err = decodePacket(buf[16:blen], res)
  if err != nil {
  return err
  }
@@ -816,15 +816,17 @@ func (c *Conn) recvLoop(conn net.Conn) error {
  switch res.Type {
  case EventNodeCreated:
  wTypes = append(wTypes, watchTypeExist)
- case EventNodeDeleted, EventNodeDataChanged:
- wTypes = append(wTypes, watchTypeExist, watchTypeData, watchTypeChild)
+ case EventNodeDataChanged:
+ wTypes = append(wTypes, watchTypeExist, watchTypeData)
  case EventNodeChildrenChanged:
  wTypes = append(wTypes, watchTypeChild)
+ case EventNodeDeleted:
+ wTypes = append(wTypes, watchTypeExist, watchTypeData, watchTypeChild)
  }
  c.watchersLock.Lock()
  for _, t := range wTypes {
  wpt := watchPathType{res.Path, t}
- if watchers := c.watchers[wpt]; watchers != nil && len(watchers) > 0 {
+ if watchers := c.watchers[wpt]; len(watchers) > 0 {
  for _, ch := range watchers {
  ch <- ev
  close(ch)