Correct handling of row-has-child-toggled signal

Correct handling of row-has-child-toggled signal

When a filter function is used that determines the visibility property
of a node using whether or it it has children, the state of this node
very likely changes when the filter model receives a
row-has-child-toggled signal.  Therefore, we need to handle state
changes in the row-has-child-toggled handler.