make sure to strip away empty fields in samplesheet

[b97pla]

• Empty fields in the sample sheet turned out to cause an exception when demultiplexing

[codecov[bot]]

Codecov Report

Base: 100% // Head: 100% // Increases project coverage by +1% :tada:

Coverage data is based on head (73be316) compared to base (67f2ad9). Patch coverage: 100% of modified lines in pull request are covered.

:exclamation: Current head 73be316 differs from pull request most recent head 9abb381. Consider uploading reports for the commit 9abb381 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #12 +/- ## ===================================== + Coverage 100% 100% +1% ===================================== Files 5 5 Lines 262 263 +1 ===================================== + Hits 261 262 +1 Misses 1 1 ``` | [Impacted Files](https://codecov.io/gh/Molmed/fastq_demux/pull/12?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Molmed) | Coverage Δ | | |---|---|---| | [fastq\_demux/parser.py](https://codecov.io/gh/Molmed/fastq_demux/pull/12?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Molmed#diff-ZmFzdHFfZGVtdXgvcGFyc2VyLnB5) | `99% <100%> (+1%)` | :arrow_up: | 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=Molmed). 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=Molmed)

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