Fix BallJointConstraint and WeldJointConstraint

`BallJointConstraint` had bug in computation of constraint impulse. For example, the closed loop in rigidLoop app showed weird behavior at the beginning of the simulation. The ball joint is passive joint but it looks like some impulse was applied to the ball joint.

This pull request fixes the incorrect computation of constraint impulse for `BallJointConstraint` and `WeldJointContraint`.