Only error on bin length filter if there are bins

[prototaxites]

Added error handling for cases with no bins passing the size filter.

PR checklist

• This comment contains a description of changes (with reason).
• If you've fixed a bug or added code that should be tested, add tests!
• If you've added a new tool - have you followed the pipeline conventions in the contribution docs
• If necessary, also make a PR on the nf-core/mag branch on the nf-core/test-datasets repository.
• Make sure your code lints (nf-core pipelines lint).
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• Usage Documentation in docs/usage.md is updated.
• Output Documentation in docs/output.md is updated.
• CHANGELOG.md is updated.
• README.md is updated (including new tool citations and authors/contributors).

[github-actions]

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[prototaxites]

@nf-core-bot fix linting

[jfy133]

Tested by breaking the megahit command, and error seen in dev is now removed in this branch, so LGTM tiny change to CHANGELOG and can merge :)

Thanks @prototaxites !