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/world/entity/monster/Shulker.java.patch

@@ -34,7 +34,7 @@
                      if (enumdirection != null) {
 +                        // CraftBukkit start
 +                        EntityTeleportEvent teleportEvent = CraftEventFactory.callEntityTeleportEvent(this, blockposition1.getX(), blockposition1.getY(), blockposition1.getZ());
-+                        if (teleportEvent.isCancelled()) {
++                        if (teleportEvent.isCancelled() || teleportEvent.getTo() == null) { // Paper
 +                            return false;
 +                        } else {
 +                            blockposition1 = CraftLocation.toBlockPosition(teleportEvent.getTo());