Blopware authored Apr 29, 2021 and Georg Krause committed May 09, 2021

For that case, the resulting saved file made use of these slashes to
store the tracks in subdirectories of federation_cache/xx/xx/xx, instead of
in the federation_cache/xx/xx/xx directory itself. As a consequence, the
tracks are downloaded in the wrong location, and upon any trial of
playing the tracks, funkwhale responds with the message
"The track cannot be loaded. You can have connectivity issues"

An example of a podcast with this kind of RSS items is located in
https://www.rtve.es/api/programas/2082/audios.rss

This commit overcomes this by a simple replacement of the offending
slashes to hyphens.