Minor Change to PocketManager

Added a minor check to PocketManager.loadDimension() so that an attempt
to load an unregistered dimension won't be passed on to Forge where it
would cause an exception - which is then caught by Forge before it can
cause problems. This isn't strictly necessary, but it's a nice
consideration.

src/main/java/StevenDimDoors/mod_pocketDim/core/PocketManager.java

@@ -483,6 +483,11 @@ public class PocketManager
 	
 	public static WorldServer loadDimension(int id)
 	{
+		if (!DimensionManager.isDimensionRegistered(id))
+		{
+			return null;
+		}
+		
 		WorldServer world = DimensionManager.getWorld(id);
 		if (world == null)
 		{