Call self.finish() before delegating to the original SIGINT handler.

        This handler should only be in place while the progress display is
        active.

def handle_sigint(self, signum, frame):
        """
        Call self.finish() before delegating to the original SIGINT handler.

        This handler should only be in place while the progress display is
        active.
        """
        self.finish()
        self.original_handler(signum, frame)