Prevent spawn location getters from allowing making the location invalid (#13831)

Author: masmc05

paper-api/src/main/java/io/papermc/paper/event/player/AsyncPlayerSpawnLocationEvent.java

@@ -53,7 +53,7 @@ public PlayerConfigurationConnection getConnection() {
      * @return the spawn location
      */
     public Location getSpawnLocation() {
-        return this.spawnLocation;
+        return this.spawnLocation.clone();
     }
 
     /**

paper-server/patches/sources/net/minecraft/server/network/config/PrepareSpawnTask.java.patch

@@ -125,7 +125,7 @@
 +                        );
 +                        ev.callEvent();
 +                        spawnPosition = io.papermc.paper.util.MCUtil.toVec3(ev.getSpawnLocation());
-+                        this.spawnLevel = ((org.bukkit.craftbukkit.CraftWorld) ev.getSpawnLocation().getWorld()).getHandle();
++                        if (ev.getSpawnLocation().getWorld() != null) this.spawnLevel = ((org.bukkit.craftbukkit.CraftWorld) ev.getSpawnLocation().getWorld()).getHandle();
 +                        this.spawnPosition = CompletableFuture.completedFuture(spawnPosition);
 +                        this.spawnAngle = new Vec2(ev.getSpawnLocation().getYaw(), ev.getSpawnLocation().getPitch());
 +                    }