Unused values in DistanceJoint's serializer

[zOadT]

The serializer of DistanceJoint saves the values of m_impulse, m_gamma and m_bias. This has no affect in the deserialize method, because their value is hard coded to zero in the constructor. This can be easily fixed by overriding the values manually after creating the joint.

To me it seems like at least m_impulse can keep a positive value afer calling initVelocityConstraints amd therefore can also have an effect on the computations, but I am not completely sure. If it would make a different we would also have to update the other joints.