Fixes#91369, where a pointer to a deleted btTypedConstraint instance
was being dereferenced, causing a crash.
What was happening was:
1. When the animation starts the first time, BKE_rigidbody_rebuild_sim
eventually calls btDiscreteDynamicsWorld::addConstraint, which in turn
will store a pointer to the btTypedConstraint in
btRigidBody::m_constraintRefs for each body in the constraint
2. When undoing, the btDynamicsWorld is deleted, then the Object
containing the btTypedConstraint (taking the btTypedConstraint with
it) - however, the pointer to the btTypedConstraint is still in the
btRigidBody!
3. When playing the animation a second time, rigidbody_update_simulation
will rebuild the simulation, which causes RB_body_delete to be called,
which iterates over all the body's m_constraintRefs and dereferences
the deleted pointer.
Co-authored-by: Eoin Mcloughlin <hkeoin@eoinrul.es>
Pull Request: https://projects.blender.org/blender/blender/pulls/126079
5ee7d02840