#14 _editFlag not reset, causes crash - easy fix.

[William F. Cook]

If the user clicks on an already-selected node and then hits F2 before the edit starts via the timer, the beginEditByUser() function is called twice. This is because _NodeTextBox._editFlag isn't being reset and the timer event handler calls the function again.

The result is that when the edit is finished a NullReferenceException is thrown in BindableControl.GetMemberAdapter().

Thanks again for this great control.