fix issue about  'hideNode()' & 'showNode()'

Issue Info:
If you use 'showNode()' method to show the node what 'nochecked' is true
and has not been hidden, the node's 'nochecked' will be false.

If you use 'hideNode()' method to hide the node what 'nochecked' is
false and has been hidden, the node's 'nochecked' will be true.