Fix a potential problem with "Entity already added" when using the dormant

chunk cache capability. The entities in the dormant chunk cache will get new
IDs prior to the cached chunk returning.

common/net/minecraftforge/common/ForgeChunkManager.java

@@ -880,7 +880,18 @@ public class ForgeChunkManager
     public static Chunk fetchDormantChunk(long coords, World world)
     {
         Cache<Long, Chunk> cache = dormantChunkCache.get(world);
-        return cache == null ? null : cache.getIfPresent(coords);
+        Chunk chunk = cache.getIfPresent(coords);
+        if (chunk != null)
+        {
+            for (List<Entity> eList : chunk.entityLists)
+            {
+                for (Entity e: eList)
+                {
+                    e.resetEntityId();
+                }
+            }
+        }
+        return chunk;
     }
 
     static void captureConfig(File configDir)

patches/minecraft/net/minecraft/entity/Entity.java.patch

@@ -138,7 +138,7 @@
      }
  
      public int func_82143_as()
-@@ -2399,4 +2441,84 @@
+@@ -2399,4 +2441,92 @@
      {
          return this.isBurning();
      }
@@ -221,5 +221,13 @@
 +        {
 +            persistentID = UUID.randomUUID();
 +        }
++    }
++
++    /**
++     * Reset the entity ID to a new value. Not to be used from Mod code
++     */
++    public final void resetEntityId()
++    {
++        this.entityId = nextEntityID++;
 +    }
  }