fix FileNotFoundError error on restart on macOS (webui.sh)

[shinshin86]

Description

Hello!

In a macOS environment, when toggling the enable/disable state of extensions in the Extension tab and pressing the Apply and restart UI button, the following error log appears in the console.
Additionally, in order for changes to extensions to take effect, I need to terminate the process and then restart the functionality.

Traceback (most recent call last):
  File "/Users/username/stable-diffusion-webui/venv/lib/python3.9/site-packages/gradio/routes.py", line 488, in run_predict
    output = await app.get_blocks().process_api(
  File "/Users/username/stable-diffusion-webui/venv/lib/python3.9/site-packages/gradio/blocks.py", line 1431, in process_api
    result = await self.call_function(
  File "/Users/username/stable-diffusion-webui/venv/lib/python3.9/site-packages/gradio/blocks.py", line 1103, in call_function
    prediction = await anyio.to_thread.run_sync(
  File "/Users/username/stable-diffusion-webui/venv/lib/python3.9/site-packages/anyio/to_thread.py", line 33, in run_sync
    return await get_asynclib().run_sync_in_worker_thread(
  File "/Users/username/stable-diffusion-webui/venv/lib/python3.9/site-packages/anyio/_backends/_asyncio.py", line 877, in run_sync_in_worker_thread
    return await future
  File "/Users/username/stable-diffusion-webui/venv/lib/python3.9/site-packages/anyio/_backends/_asyncio.py", line 807, in run
    result = context.run(func, *args)
  File "/Users/username/stable-diffusion-webui/venv/lib/python3.9/site-packages/gradio/utils.py", line 707, in wrapper
    response = f(*args, **kwargs)
  File "/Users/username/stable-diffusion-webui/modules/ui_extensions.py", line 54, in apply_and_restart
    restart.restart_program()
  File "/Users/username/stable-diffusion-webui/modules/restart.py", line 17, in restart_program
    (Path(script_path) / "tmp" / "restart").touch()
  File "/Users/username/.rye/py/cpython@3.9.18/install/lib/python3.9/pathlib.py", line 1315, in touch
    fd = self._raw_open(flags, mode)
  File "/Users/username/.rye/py/cpython@3.9.18/install/lib/python3.9/pathlib.py", line 1127, in _raw_open
    return self._accessor.open(self, flags, mode)
FileNotFoundError: [Errno 2] No such file or directory: '/Users/username/stable-diffusion-webui/tmp/restart'

This error occurs due to the absence of the tmp/restart file. Upon reviewing the webui.sh script, I noticed it lacks a process to create the tmp directory.
This process is present in the webui.bat file, so I believe it's necessary to add it to webui.sh as well.

I've only tested this on a local Apple Silicon macOS environment.
I assume the webui.sh script is also used on Linux systems. If the changes are unnecessary on a Linux environment, could you let me know.
(I've only been able to test on macOS).

Best regards!

Checklist:

• I have read contributing wiki page
• I have performed a self-review of my own code
• My code follows the style guidelines
• My code passes tests
  I have read the following documentation but could not perform the test...
  Am I correct in understanding that this is to start a Web UI instance with a specific command and then run tests on it?
  https://github.com/AUTOMATIC1111/stable-diffusion-webui/wiki/Tests

[AUTOMATIC1111]

made ad3b8a1 as an alternative solution which only makes the dir when it's needed

[shinshin86]

Thanks for the confirmation. Got it!