Filtering macs2 files without peaks

[JoseEspinosa]

As explained in #128 when macs2 files have any peak inside an exception is raised.

Closes #128

PR checklist

• This comment contains a description of changes (with reason)
• Ensure the test suite passes (nextflow run . -profile test,docker).
• Make sure your code lints (nf-core lint .).
• CHANGELOG.md is updated

[JoseEspinosa]

Have drafted this PR by the moment, although the data in issue #128 is no longer available, I guess you also don't have it @drpatelh 🙄
If not we may need in slack for it

[drpatelh]

Yep, maybe we ask Pablo on Slack. Wonder if we can sub-sample the test data quite heavily to reproduce? 🤔

[drpatelh]

Nice! You found a real dataset to test with?

[JoseEspinosa]

I mixed a file from Pablo with our test-dataset but I think it might be safer than someone else give it a try