Initialize the world transform to identity for btCollisionObject/btRigidBody.

Some developers only initialize the world position, and not the orientation -> uninitialized data. 

We should probably add some warning in btTransform, in debug mode. Note we don't initialize btTransform/btQuaternion/btVector3/btMatrix3x3 default constructor, for performance reasons.

src/BulletCollision/CollisionDispatch/btCollisionObject.cpp

@@ -37,7 +37,7 @@ btCollisionObject::btCollisionObject()
 		m_ccdMotionThreshold(btScalar(0.)),
 		m_checkCollideWith(false)
 {
-	
+	m_worldTransform.setIdentity();
 }
 
 btCollisionObject::~btCollisionObject()