If a URL fails to decode, keep going

May want to use ValueError to be even more forgiving. Also could put add() in an else block?

```python
try:
  found_url = ...
except ValueError as e:
  logging.warning('Error decoding url: %s. %s: %s', link['absurl'], e.__class__.__name__, e)
else:
  result.add(found_url)
```