fix: document joiner division by zero with distribution based rank fusion

[AnesBenmerzoug]

Related Issues

Proposed Changes:

• This PR fixes an issue with the distribution based rank fusion join mode of the DocumentJoiner class when an empty list of documents is passed.
• It additionally fixes division by zero errors when no document list is passed to the merge and rrf join modes.

How did you test it?

• Locally by running hatch test -- test/components/joiners/test_document_joiner.py

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.
• I documented my code
• I ran pre-commit hooks and fixed any issue

[CLAassistant]

All committers have signed the CLA.

[silvanocerza]

Nice PR, thanks! 🙏

[coveralls]

Pull Request Test Coverage Report for Build 11836294015

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.007%) to 90.184%

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Totals
Change from base Build 11799929241:	0.007%
Covered Lines:	7782
Relevant Lines:	8629

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💛 - Coveralls