string index out of range

```
  File "venv/lib/python3.10/site-packages/precise_bbcode/bbcode/defaults/tag.py", line 114, in render
    if href[0] == href[-1] and href[0] in ('"', '\'') and len(href) > 2:

Exception Type: IndexError at /
Exception Value: string index out of range
```

Happens with short hrefs.
I'll fix it in a moment.