Fix dupe uuid check on entity add (#6735)

patches/server/Duplicate-UUID-Resolve-Option.patch

@@ -173,9 +173,10 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
      private boolean addEntityUuid(T entity) {
          if (!this.knownUuids.add(entity.getUUID())) {
 +            // Paper start
-+            if (((Entity) entity).isRemoved()) {
-+                stopTracking(entity); // remove the existing entity
-+                return false;
++            T conflict = this.visibleEntityStorage.getEntity(entity.getUUID());
++            if (conflict != null && ((Entity) conflict).isRemoved()) {
++                stopTracking(conflict); // remove the existing entity
++                return true;
 +            }
 +            // Paper end
              PersistentEntitySectionManager.LOGGER.warn("UUID of added entity already exists: {}", entity);