Fix: handle metaphlan profiles with unclassified taxa in the lineage

[Midnighter]

Problem was report on Slack.

[sofstam]

Wondering why the tests fail though.

[Midnighter]

I'll fix the test error on Windows.

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.10 :tada:

Comparison is base (6fd72cb) 81.98% compared to head (6bdfd4b) 82.08%.

:exclamation: Current head 6bdfd4b differs from pull request most recent head 4849759. Consider uploading reports for the commit 4849759 to get more accurate results

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #61 +/- ## ========================================== + Coverage 81.98% 82.08% +0.10% ========================================== Files 104 104 Lines 1565 1574 +9 Branches 131 133 +2 ========================================== + Hits 1283 1292 +9 Misses 241 241 Partials 41 41 ``` | [Impacted Files](https://codecov.io/gh/taxprofiler/taxpasta/pull/61?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None) | Coverage Δ | | |---|---|---| | [...phlan/metaphlan\_profile\_standardisation\_service.py](https://codecov.io/gh/taxprofiler/taxpasta/pull/61?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-c3JjL3RheHBhc3RhL2luZnJhc3RydWN0dXJlL2FwcGxpY2F0aW9uL21ldGFwaGxhbi9tZXRhcGhsYW5fcHJvZmlsZV9zdGFuZGFyZGlzYXRpb25fc2VydmljZS5weQ==) | `100.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None)

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