Fix setVelocity infinite regress crash

[Myst1cS04p]

Added a guard flag to BukkitPlayer.setVelocity and PlayerKnockbackListener.onPlayerVelocity.
Hopefully ts guard flag will stop ts plugin from looping endlessly and crashing the server

[Axionize]

What crash? Why is velocity infinite? Do you have reproductions steps for me?

[Myst1cS04p]

I did ts a while ago so I'm not even sure what happened. No clue how to replicate, all I know is that the velo gets set to infinity sometimes and crashes the server. There's a full traceback below, but I ran ts on my server and it seemed stable so I opened the pr.

Callback:

[12:49:46] [Watchdog Thread/ERROR]: ------------------------------
[12:49:46] [Watchdog Thread/ERROR]: The server has stopped responding! This is (probably) not a Purpur bug.
[12:49:46] [Watchdog Thread/ERROR]: If you see a plugin in the Server thread dump below, then please report it to that author
[12:49:46] [Watchdog Thread/ERROR]: 	 *Especially* if it looks like HTTP or MySQL operations are occurring
[12:49:46] [Watchdog Thread/ERROR]: If you see a world save or edit, then it means you did far more than your server can handle at once
[12:49:46] [Watchdog Thread/ERROR]: 	 If this is the case, consider increasing timeout-time in spigot.yml but note that this will replace the crash with LARGE lag spikes
[12:49:46] [Watchdog Thread/ERROR]: If you are unsure or still think this is a Purpur bug, please report this to https://github.com/PurpurMC/Purpur/issues
[12:49:46] [Watchdog Thread/ERROR]: Be sure to include ALL relevant console errors and Minecraft crash reports
[12:49:46] [Watchdog Thread/ERROR]: Purpur version: 1.21.8-2497-a49cdb9 (MC: 1.21.8)
[12:49:46] [Watchdog Thread/ERROR]: ------------------------------
[12:49:47] [Watchdog Thread/ERROR]: During the run of the server, a plugin set an excessive velocity on an entity
[12:49:47] [Watchdog Thread/ERROR]: This may be the cause of the issue, or it may be entirely unrelated
[12:49:47] [Watchdog Thread/ERROR]: Excessive velocity set detected: tried to set velocity of entity TPplayz2025 id #353749 to (0.0,4.307523987199999,0.0).
[12:49:47] [Watchdog Thread/ERROR]: 		org.bukkit.craftbukkit.entity.CraftEntity.setVelocity(CraftEntity.java:223)
[12:49:47] [Watchdog Thread/ERROR]: 		knockbacksync-bukkit-1.3.6-dev-b125.jar//me.caseload.knockbacksync.player.BukkitPlayer.setVelocity(BukkitPlayer.java:193)
[12:49:47] [Watchdog Thread/ERROR]: 		knockbacksync-bukkit-1.3.6-dev-b125.jar//me.caseload.knockbacksync.listener.PlayerKnockbackListener.onPlayerVelocity(PlayerKnockbackListener.java:53)
[12:49:47] [Watchdog Thread/ERROR]: 		knockbacksync-bukkit-1.3.6-dev-b125.jar//me.caseload.knockbacksync.listener.bukkit.BukkitPlayerKnockbackListener.onPlayerVelocity(BukkitPlayerKnockbackListener.java:38)
[12:49:47] [Watchdog Thread/ERROR]: 		co.aikar.timings.TimedEventExecutor.execute(TimedEventExecutor.java:80)
[12:49:47] [Watchdog Thread/ERROR]: 		org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:71)
[12:49:47] [Watchdog Thread/ERROR]: 		io.papermc.paper.plugin.manager.PaperEventManager.callEvent(PaperEventManager.java:54)
[12:49:47] [Watchdog Thread/ERROR]: 		io.papermc.paper.plugin.manager.PaperPluginManagerImpl.callEvent(PaperPluginManagerImpl.java:131)
[12:49:48] [Watchdog Thread/ERROR]: 		org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:628)
[12:49:48] [Watchdog Thread/ERROR]: 		org.bukkit.event.Event.callEvent(Event.java:46)
[12:49:48] [Watchdog Thread/ERROR]: 		net.minecraft.server.level.ServerEntity.sendChanges(ServerEntity.java:268)
[12:49:48] [Watchdog Thread/ERROR]: 		net.minecraft.server.level.ChunkMap.newTrackerTick(ChunkMap.java:1016)
[12:49:48] [Watchdog Thread/ERROR]: 		net.minecraft.server.level.ChunkMap.tick(ChunkMap.java:1025)
[12:49:49] [Watchdog Thread/ERROR]: 		net.minecraft.server.level.ServerChunkCache.tick(ServerChunkCache.java:500)
[12:49:49] [Watchdog Thread/ERROR]: 		net.minecraft.server.level.ServerLevel.tick(ServerLevel.java:791)
[12:49:49] [Watchdog Thread/ERROR]: 		net.minecraft.server.MinecraftServer.tickChildren(MinecraftServer.java:1762)
[12:49:49] [Watchdog Thread/ERROR]: 		net.minecraft.server.MinecraftServer.tickServer(MinecraftServer.java:1567)
[12:49:49] [Watchdog Thread/ERROR]: 		net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1283)
[12:49:49] [Watchdog Thread/ERROR]: 		net.minecraft.server.MinecraftServer.lambda$spin$2(MinecraftServer.java:313)
[12:49:49] [Watchdog Thread/ERROR]: 		java.base/java.lang.Thread.run(Thread.java:1583)
[12:49:49] [Watchdog Thread/ERROR]: ------------------------------