Fix slip calculation in DryFrictionWheelJoint

[juliusaka]

The previous implementation lead to an error because of 1/sqrt(0) in Dymola 2025x using the dassl solver.

[juliusaka]

We (@lmikelsons and me) did some more research about this. This isn't a problem due to 2025x, its about the analytic Jacobian calculation (which I turned on Dymola 2025x).

For the case with the 0.0001 outside the brackets of sqrt, within the Jacobian section we have

DYNX(DYNhelp,164) = sqrtGuarded(DYNX(DYNhelp,162)+DYNX(DYNhelp,163),

which can lead to a division by zero error:

Error: The following error was detected at time: 0.00018

Model error - division by zero: (1.0) / (sqrt(chassis.dryFrictionWheelJoint.v_slip_long^2+chassis.dryFrictionWheelJoint.v_slip_lat^2)) = (1) / (0)

With the 0.0001^2 inside the brackets, we get

DYNX(DYNhelp,164) = sqrtGuarded(1E-08+DYNX(DYNhelp,162)+DYNX(DYNhelp,163),

in the Jacobian section and the model runs.