Sets iter to the currently selected node if selection is set to
GTK_SELECTION_SINGLE or GTK_SELECTION_BROWSE. iter may be NULL if you
just want to test if selection has any selected nodes. model is filled
with the current model as a convenience. This function will not work if you
use selection is GTK_SELECTION_MULTIPLE.
Sets iter to the currently selected node if selection is set to GTK_SELECTION_SINGLE or GTK_SELECTION_BROWSE. iter may be NULL if you just want to test if selection has any selected nodes. model is filled with the current model as a convenience. This function will not work if you use selection is GTK_SELECTION_MULTIPLE.