wx.lib.mixins.listctrl.TextEditMixin: Fixed the double END_LABEL_EDIT

wx.lib.mixins.listctrl.TextEditMixin: Fixed the double END_LABEL_EDIT
event problem in TextEditMixin by checking if the editor was already
hidden before continuing with the CloseEditor method.  Also added code
to OpenEditor to send the BEGIN_LABEL_EDIT event and to not allow the
opening of the editor to continue if the event handler doesn't allow
it.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@39333 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775