also add serializeContactManifolds to btSoftMultiBodyDynamicsWorld.cpp and btDiscreteDynamicsWorld.

src/BulletDynamics/Dynamics/btDiscreteDynamicsWorld.cpp

@@ -1533,6 +1533,8 @@ void	btDiscreteDynamicsWorld::serialize(btSerializer* serializer)
 
 	serializeRigidBodies(serializer);
 
+	serializeContactManifolds(serializer);
+
 	serializer->finishSerialization();
 }
 

src/BulletSoftBody/btSoftMultiBodyDynamicsWorld.cpp

@@ -361,6 +361,8 @@ void	btSoftMultiBodyDynamicsWorld::serialize(btSerializer* serializer)
 
 	serializeCollisionObjects(serializer);
 
+	serializeContactManifolds(serializer);
+
 	serializer->finishSerialization();
 }