Handles when the current index of the combobox changes.

def path_selection_changed(self):
        """Handles when the current index of the combobox changes."""
        idx = self.currentIndex()
        if idx == SELECT_OTHER:
            external_path = self.select_directory()
            if len(external_path) > 0:
                self.add_external_path(external_path)
                self.setCurrentIndex(self.count() - 1)
            else:
                self.setCurrentIndex(CWD)
        elif idx == CLEAR_LIST:
            reply = QMessageBox.question(
                    self, _("Clear other directories"),
                    _("Do you want to clear the list of other directories?"),
                    QMessageBox.Yes | QMessageBox.No)
            if reply == QMessageBox.Yes:
                self.clear_external_paths()
            self.setCurrentIndex(CWD)
        elif idx >= EXTERNAL_PATHS:
            self.external_path = to_text_string(self.itemText(idx))