flake8 crashes when any undefined token ends in dot (.), an incomplete attribute

MWE

```
if __name__ == "__main__":
    foo.
```

I know this doesn't seem like it would occur very often, but it seems to happen to me lot.  It's something about trying to get completion to work, and when that fails, I usually have to stop and do some thinking or research, and while I'm doing that, my DE checks what I wrote and, bingo, I get this error.