Fixed memory leak in Bullet shape model (#3180)

  /**

   * Desctructor

   */

  BulletDskShape::~BulletDskShape() { }

  BulletDskShape::~BulletDskShape() {

    // Bullet does not clean up the mesh automatically, so we need to delete it manually

    if (m_mesh) {

      for (int i = 0; i < m_mesh->getIndexedMeshArray().size(); i++) {

        btIndexedMesh &v_mesh = m_mesh->getIndexedMeshArray()[i];

        delete[] v_mesh.m_triangleIndexBase;

        v_mesh.m_triangleIndexBase = nullptr;

        delete[] v_mesh.m_vertexBase;

        v_mesh.m_vertexBase = nullptr;

      }

    }

  }

  /**