Fix a TypeError when deleting the watched folder on Windows

[BoboTiG]

On Windows, if one deleted the watched folder (or had no enough rights to use it), that error poped out:

Exception in thread Thread-1:
Traceback (most recent call last):
File "watchdog\observers\winapi.py", line 333, in read_directory_changes
    ctypes.byref(nbytes), None, None)
File "watchdog\observers\winapi.py", line 105, in _errcheck_bool
    raise ctypes.WinError()
PermissionError: [WinError 5] Access refused.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "C:\Python37-32\lib\threading.py", line 926, in _bootstrap_inner
    self.run()
File "watchdog\observers\api.py", line 145, in run
    self.queue_events(self.timeout)
File "watchdog\observers\read_directory_changes.py", line 76, in queue_events
    winapi_events = self._read_events()
File "watchdog\observers\read_directory_changes.py", line 73, in _read_events
    return read_events(self._handle, self.watch.path, self.watch.is_recursive)
File "watchdog\observers\winapi.py", line 387, in read_events
    buf, nbytes = read_directory_changes(handle, path, recursive)
File "watchdog\observers\winapi.py", line 340, in read_directory_changes
    return _generate_observed_path_deleted_event()
File "watchdog\observers\winapi.py", line 298, in _generate_observed_path_deleted_event
    event = FILE_NOTIFY_INFORMATION(0, FILE_ACTION_DELETED_SELF, len(path), path.value)
TypeError: expected bytes, str found

I added a non-regression test and used a non-ASCII path to ensure there is no unicode issue as well.