fix headless: ensure imsave_thread is finished before quitting

from pathlib import Path

import subprocess

from functools import partial

import time

from qtpy.QtWidgets import QAction, QFileDialog, QMenu, QHBoxLayout, QVBoxLayout, QApplication, QStackedWidget, QSplitter, QListWidget, QShortcut, QListWidgetItem, QMessageBox, QTextEdit, QPlainTextEdit

from qtpy.QtCore import Qt, QPoint, QSize, QEvent, Signal

    def run_next_dir(self):

        if len(self.exec_dirs) == 0:

            while self.imsave_thread.isRunning():

                time.sleep(0.1)

            LOGGER.info(f'finished translating all dirs, quit app...')

            self.app.quit()

            return