[MC-129644] Underwater ruin structure files cannot be found

When patching from 18w16a to 18w20a, several objects failed to load and the chunk failed to save.

Console Logs

 [17:24:05] [Server thread/ERROR]: Couldn't load structure minecraft:ruin/ruin5_brick: java.io.FileNotFoundException: minecraft:structures/ruin/ruin5_brick.nbt
 [17:24:05] [Server thread/ERROR]: Couldn't load structure minecraft:ruin/ruin5_cracked: java.io.FileNotFoundException: minecraft:structures/ruin/ruin5_cracked.nbt
 [17:24:05] [Server thread/ERROR]: Couldn't load structure minecraft:ruin/ruin5_mossy: java.io.FileNotFoundException: minecraft:structures/ruin/ruin5_mossy.nbt
 [17:24:08] [Server thread/ERROR]: Couldn't load structure minecraft:ruin/ruin1_brick: java.io.FileNotFoundException: minecraft:structures/ruin/ruin1_brick.nbt
 [17:24:08] [Server thread/ERROR]: Couldn't load structure minecraft:ruin/ruin1_cracked: java.io.FileNotFoundException: minecraft:structures/ruin/ruin1_cracked.nbt
 [17:24:08] [Server thread/ERROR]: Couldn't load structure minecraft:ruin/ruin1_mossy: java.io.FileNotFoundException: minecraft:structures/ruin/ruin1_mossy.nbt