slugify: check iconv error, refs #9855
slugify: check iconv error, refs #9855

iconv() returns `FALSE` when there is a failure, which was happening
consistently in our Alpine-based Docker image as musl's iconv does not support
`//TRANSLIT`. This commit gives it a second shot without `//TRANSLIT`` or
ignore otherwise.

artefactual/atom,artefactual/atom,artefactual/atom