[hts-nim] error adding to csi index
Hi,
I'm receiving an error saying:

```
$ mosdepth -b ../../../../reference/ref.fasta.bed -t 2 -n -x prefix PS-A1.bam
[E::hts_idx_check_range] Region 977930..1679516 cannot be stored in a csi index with min_shift = 14, n_lvls = 2. Try using min_shift = 14, n_lvls >= 3
[hts-nim] error adding to csi index
```
Which leaves me clueless on where to start debugging.
Should I check the format of my bed file (it's supposed to reflect the intervals for each chromosome)? First lines:
```
VACF01000001.1  0       977930
VACF01000002.1  977930  1679516
VACF01000003.1  1679516 2235559
VACF01000004.1  2235559 2496722
VACF01000005.1  2496722 2609266
```
Thanks
/Johan

