empty variant collection when loading strelka vcf

[timodonnell]

Loading the below strelka shared strelka VCF, I seem to get an empty variant collection back.

>> vc = varcode.VariantCollection("/Users/tim/Box Sync/pt189/variants/strelka-somatic-primary-illumina-exome/passed.somatic.snvs.vcf")
>> len(vc)
0

[iskandr]

The filter column for these VCFs is getting parsed as absent (no clue why, it's "PASS" in the file). Changed the parsing logic to allow empty filter values as if they were "PASS".