fix espeak engine: ReferenceError: weakly-referenced object no longer exists

[Jiangshan00001]

Describe the bug A clear and concise description of what the bug is.

To Reproduce Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior A clear and concise description of what you expected to happen.

Screenshots If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context Add any other context about the problem here.

test_save_to_file start test_save_to_file finish.file saved to: /workspaces/codespaces-blank/test.wav Exception ignored on calling ctypes callback function: <bound method EspeakDriver._onSynth of <pyttsx4.drivers.espeak.EspeakDriver object at 0x7f093c49b460>> Traceback (most recent call last): File "/workspaces/codespaces-blank/pyttsx4/drivers/espeak.py", line 193, in _onSynth self._proxy.notify('finished-utterance', completed=True) ReferenceError: weakly-referenced object no longer exists

[Jiangshan00001]

fixed