Softbody Anchors on Kinematic RigidBody cause division by zero

[fredUmlaut]

In btSoftBody::solveConstraints() for 'Prepare anchors' a Impulse Matrix gets calculated for each anchor.

If the current anchor body is a Kinematic RigidBody (which has a mass of 0 and no inertiaTensor) this causes a division by zero in btMatrix3x3::inverse() which is called from ImpulseMatrix(..)