Fix checksum and bug in irc_disentangle dataset
_The documentation is not available anymore as the PR was closed or merged._
There was a bug in filepath segment: 
- wrong: `jkkummerfeld-irc-disentanglement-fd379e9`
- right: `jkkummerfeld-irc-disentanglement-35f0a40`

Also there was a bug in the checksum of the downloaded file.

This PR fixes these issues.

Fix partially #4376.
