Some gff3 files from genbank can have blank lines at the end. This adds a check that each line in a gff file has enough tokens to have start and end coords, and skips the line if not.
On short genomes such as viral, the start coord can go negative for variants near position 1 with sizable flank sizes (or not so sizable, depending). This enforces a min start coord of 1. The end coord fix is TBD