Fix lock hang on Windows

[TheMatt2]

Solves an issue where FileLock and SoftFileLock could hang sit in an infinite loop if PermissionError or OSError is encountered on Windows while trying to lock the file.

Originally mentioned on #147.

On Windows, if the name of the file given is invalid, such as forgetting to to double backspace on windows, the EINVAL message is not accounted for in the error handling.

import filelock

filename = "C:\path\to\lock\but\backslash\is\not\escaped"
with filelock.FileLock(filename):
    pass # waits forever and never completes

If you had just tried to open the file, you would see the following message:

filename = "C:\path\to\lock\but\backslash\is\not\escaped"
f = open(filename)

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [Errno 22] Invalid argument: 'C:\\path\to\\lock\x08ut\x08ackslash\\is\not\\escaped'

The issue that is being danced around is it seems PermissionError will randomly occur on os.open() when trying to open the lock file. I have been unable to figure out why Windows raises PermissionError, but that seems somewhat a mute point.

https://github.com/tox-dev/py-filelock/blob/dceb9e5b7e4edd232435521f20efe189fe88f71b/src/filelock/_windows.py#L24-L28

The problem is any error raised, other than the one explicitly handled, ignoring other errors.
This is corrected by ignoring some explicit errors, but allowing other errors to be raised.

This also adds a check for if the path of the lock file is a directory. On Windows, trying to open a path that is a directory as a file would raise a PermissionError that can't be differentiated from the exception that is sometimes raised from just trying to open the file in the middle of a bunch of locking and unlocking.

Renamed utils.raise_on_exist_ro_file(filename) to utils.raise_unwritable_file(filename) to better describe what is does, now that the directory check has been added to it.

[TheMatt2]

Yes, flake. "unwritable" is a word...

[TheMatt2]

I'm actually not sure why I'm getting the flake8 error

tests/test_filelock.py:137:2: PT006 wrong name(s) type in @pytest.mark.parametrize, expected tuple

Anyone have suggestions? Found it

https://github.com/m-burst/flake8-pytest-style/blob/master/docs/rules/PT006.md

Should be formatted as a tuple... which I didn't know pytest supported. Go figure.