do not try to add alt sequences if there is no coverage at an anchor
do not try to add alt sequences if there is no coverage at an anchor

jts/nanopolish,rmp/nanopolish,jts/nanopolish,mateidavid/nanopolish,mateidavid/nanopolish,mateidavid/nanopolish,simpsonlab/nanopolish,simpsonlab/nanopolish,mateidavid/nanopolish,rmp/nanopolish,rmp/nanopolish,mateidavid/nanopolish,jts/nanopolish,jts/nanopolish,simpsonlab/nanopolish,rmp/nanopolish,simpsonlab/nanopolish,jts/nanopolish