Fix NPE on null loc for EntityTeleportEvent

EntityTeleportEvent#setTo is marked as nullable and so is the
getTo method. This fixes the handling of a null "to" location
by treating it the same as the event being cancelled. This is
already existing behavior for the EntityPortalEvent (which
extends EntityTeleportEvent).

paper-server/patches/sources/net/minecraft/server/commands/TeleportCommand.java.patch

@@ -20,7 +20,7 @@
  
  public class TeleportCommand {
  
-@@ -167,7 +173,30 @@
+@@ -167,7 +173,31 @@
              float f4 = Mth.wrapDegrees(f2);
              float f5 = Mth.wrapDegrees(f3);
  
@@ -33,9 +33,10 @@
 +                Location to = new Location(world.getWorld(), d3, d4, d5, f4, f5);
 +                EntityTeleportEvent event = new EntityTeleportEvent(target.getBukkitEntity(), target.getBukkitEntity().getLocation(), to);
 +                world.getCraftServer().getPluginManager().callEvent(event);
-+                if (event.isCancelled()) {
++                if (event.isCancelled() || event.getTo() == null) { // Paper
 +                    return;
 +                }
++                to = event.getTo(); // Paper - actually track new location
 +
 +                d3 = to.getX();
 +                d4 = to.getY();