Commas in srcset-URLs are not handled correctly

Although #243 is merged, srcset-URLs with commas in them are still not parsed/rewritten correctly, see https://web.archive.org/web/*/https://orf.at/ for example.

The original URLs used in srcset attributes look like this: `https://assets.orf.at/mims/2022/03/26/crops/w=875,q=90/1204287_opener_429226_coronavirus_schule_tests_vorschau_v1_a.jpg?s=bad56ac4b6df02892d3bd744c8e9494d4fd72b50`.

a complete srcset example used in this site:
```

```
results in (see [here](https://web.archive.org/web/20220114214021/https://orf.at/stories/3243632/)):
```

```