Attached Jumpthru downwarp when disappearing

[catapillie]

Attached Jumpthrus seem to warp the player down when they disappear, notably when connected to a moveblock which is destroyed by a Communal Helper moveblock redirect.

Found by @pazkallan on the Celeste discord.
Video : https://cdn.discordapp.com/attachments/429775320720211968/1504335148056051712/downwarp.mp4?ex=6a074588&is=6a05f408&hm=c9ae3cae2bda8eae079c60845073aa5f5625ac1b67addeb442239824ea615f3f&