ISSUE-299: Fixing first offsets retrieval for compacted topic

[iliax]

• [ ] Breaking change? (if so, please describe the impact and migration path for existing application instances)

What changes did you make? (Give an overview) Fixes #299 Fixes #319

Is there anything you'd like reviewers to focus on?

How Has This Been Tested? (put an "x" (case-sensitive!) next to an item)

• [ ] No need to
• [x] Manually (please, describe, if necessary)
• [x] Unit checks
• [ ] Integration checks
• [ ] Covered by existing automation

Checklist (put an "x" (case-sensitive!) next to all the items, otherwise the build will fail)

• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation (e.g. ENVIRONMENT VARIABLES)
• [x] My changes generate no new warnings (e.g. Sonar is happy)
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] Any dependent changes have been merged

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