Bcftools fails in pipeline without being caught

Delete the FORMAT lines in the header, and import a VCF so you get errors like:

```
[W::vcf_parse_format_dict2] FORMAT 'AD' at NC_000003.12:10017624 is not defined in the header, assuming Type=String
```

Then removes it. Pipeline after dies with:

```
[E::vcf_format] Invalid BCF, the FORMAT tag id=2 at NC_000003.12:10017624 not present in the header
[flush_buffer] Error: cannot write to -
Failed to read from standard input: unknown file type
```

But this is not caught so pipeline looks like it is still running, rather than error