[ROS2] Ackermann Drive Plugin fails silently if the wheels have gemetries other than SphereShape or CylinderShape

[SivertHavso]

Description

gazebo_ros_ackermann_drive should warn users if the wheel radius is an invalid value.

The plugin finds the radius by calling GetRadius() on sphere and cylinder objects but this fails silently if the wheel geometry is a mesh.

Screenshots
The relevant parts of the code is:

  impl_->wheel_radius_ = impl_->CollisionRadius(
    impl_->joints_[GazeboRosAckermannDrivePrivate::REAR_RIGHT]->GetChild()->GetCollision(id));

double GazeboRosAckermannDrivePrivate::CollisionRadius(const gazebo::physics::CollisionPtr & _coll)
{
  if (!_coll || !(_coll->GetShape())) {
    return 0;
  }
  if (_coll->GetShape()->HasType(gazebo::physics::Base::CYLINDER_SHAPE)) {
    gazebo::physics::CylinderShape * cyl =
      dynamic_cast<gazebo::physics::CylinderShape *>(_coll->GetShape().get());
    return cyl->GetRadius();
  } else if (_coll->GetShape()->HasType(gazebo::physics::Base::SPHERE_SHAPE)) {
    gazebo::physics::SphereShape * sph =
      dynamic_cast<gazebo::physics::SphereShape *>(_coll->GetShape().get());
    return sph->GetRadius();
  }
  return 0;
}

The return value from the CollisionRadius() method is never checked.

Expected behavior

The limitation should be documented, and the plugin should output an error if impl_->wheel_radius_ is 0 or negative.

Additional context
I'll attempt to make a pull request to fix it soon

[Yadunund]

@SivertHavso I have opened this PR to address the problem.