Multibody memory invalid writing

Related #2233

src/BulletDynamics/Featherstone/btMultiBody.cpp

@@ -344,6 +344,7 @@ void btMultiBody::finalizeMultiDof()
 	m_deltaV.resize(6 + m_dofCount);
 	m_realBuf.resize(6 + m_dofCount + m_dofCount * m_dofCount + 6 + m_dofCount);  //m_dofCount for joint-space vels + m_dofCount^2 for "D" matrices + delta-pos vector (6 base "vels" + joint "vels")
 	m_vectorBuf.resize(2 * m_dofCount);                                           //two 3-vectors (i.e. one six-vector) for each system dof	("h" matrices)
+	m_matrixBuf.resize(m_links.size() + 1);
 	for (int i = 0; i < m_vectorBuf.size(); i++)
 	{
 		m_vectorBuf[i].setValue(0, 0, 0);