Kipoi-veff fails silently when the input files don't exist

[Avsecz]

The following command fails silently:

kipoi veff score_variants DeepBind/Homo_sapiens/TF/D00328.018_ChIP-seq_CTCF \
>    --dataloader_args='{"fasta_file": "input/hg19.chr22.fa"}' \
>    -i input/clinvar_20180429.chr22.pathogenic.vcf.gz \
>    -s ref alt diff \
>    -o /tmp/annotated.vcf

I executed it in the root of https://github.com/kipoi/examples where the file input/... doesn't exist.

[krrome]

I assume this a duplication of / at least related to: kipoi/kipoi#314

[krrome]

copy of #18