"Out of memory" if the BED file has track lines
When trying mosdepth on a machine with 128G RAM (of which 123 free) I get an "out of memory" error with no additional explanation. The reason lies in the BED file being used, which has one track for display in the UCSC genome browser:

```
track name='Gene panel' description='Regions of interest'
```

Removing the line allows the calculation to proceed.