Casting and live TV, fixed on Android

The receiving device was blocking the stream itself. Android's network policy allows plain http to loopback only, and a cast arrives from a bare address on the local network that there is no way to name in that file. Neither end could see it - the sending machine was told the film was fine, so the only symptom was a spinner on the television.

Fixes

• Casting to an Android TV works.
• Live TV channels served over plain http play on Android, for the same reason.
• A failed cast now names the right machine: "The device this was cast from couldn't be reached - check it is still on and on this network", instead of a message that sent you to the Sources screen over a television that had gone to sleep.
• Windows builds again. mpv and ffmpeg are fetched under their renamed upstream assets, and the translation scripts no longer build broken paths out of a file URL.