do not segfault when fai_fetch fails
do not segfault when fai_fetch fails

mateidavid/nanopolish,jts/nanopolish,mateidavid/nanopolish,jts/nanopolish,mateidavid/nanopolish,jts/nanopolish,jts/nanopolish,mateidavid/nanopolish,jts/nanopolish,mateidavid/nanopolish