Horse Spawners crash 1.7 clients on a 1.8 server

[alexsosnovsky]

Describe the bug, provide any errors
If a 1.8.9 server has a horse spawner with SpawnData, any 1.7.10 client will crash upon rendering this spawner, due to a NPE: https://paste.gg/p/anonymous/8de590ae721946f8985a76df07f5b06d

This happens due to a bug with versions prior to 1.8, documented here: https://bugs.mojang.com/browse/MC-27442

How can we reproduce it?
Steps to reproduce the behavior:

1. Join a 1.8 server (which has the latest ViaVersion & ViaRewind) using a 1.8.9 client.
2. Generate a horse spawner by pasting the following into a command block, then activate the block.

/setblock ~ ~ ~ minecraft:mob_spawner 0 replace {EntityId:EntityHorse,SpawnData:{Type:0,SaddleItem:{id:saddle},Variant:0,ArmorItem:{id:golden_horse_armor}}}

3. Close Minecraft, rejoin the server using a 1.7.10 client.
4. Your 1.7.10 client will crash as soon as it loads the horse spawner.

Expected behaviour
The 1.7.10 client ideally wouldn't crash upon loading the horse spawner. I believe the simplest way to do this would be to send the 1.7 client a cow spawner (or another approximate mob) instead of any spawner with the EntityHorse entity ID. The client would render the cow spawner without triggering the NPE; this would not affect spawning logic since it is handled by the server.

ViaVersion Dump
https://dump.viaversion.com/ccd40ca12b10729b877d884baae3a3f0cedd0318a1525572cccef89e9b230b8d

Additional server info
The server runs on Paper and has FAWE, Multiverse, and NBTEditor installed, along with ViaVersion and ViaRewind.