The chrx_het_hom column has no values

[Nicolai-vKuegelgen]

Describe the bug

When using ngs-chew serve on a collection of npz-files the chrx_het_hom column of the calculated dataframe has no values (all entries are None) and the corresponding column/variable in the dash app ("het/hom calls on chrX") can also not be used.

To Reproduce
Using ngs-chew 0.9.2. (+ dash / dash-bootstrap-components 1.5)
Steps to reproduce the behavior:

1. run ngs-chew serve --strip-suffix suffix ped_example.ped *.npz
2. The "chrx_het_hom" column in the logged data frame will only show 'None'
3. The "het/hom calls on chrX" column/variable in the dash app is empty

Expected behavior
The values should be calculated and available.

[holtgrewe]

Our chrX calls are too few (864). Probably that can't be helped and the chrX fraction of reads is more informative. We should probably just remove writing out that feature.