Accommodate for missing GQ field in vcf file

[eliottBo]

Describe the solution you'd like
We added a new mitochondrial-specific variant caller to the Nallo pipeline and when uploading a vcf to Scout stage, the Genotype quality (GQ) shows as -1 as the field is missing from the vcf file.

Describe alternatives you've considered
Ideally we would like to not have a value or N/A or something of the sort to avoid confusion for the user.

[dnil]

This is the same as for all missing FORMAT values (as per characteristic CyVCF2 style). The users are likely rather used to it. That said, it is perhaps not super nice, so we'll take a look at it at low priority!