Fix parameter inlining for delayed expressions

If we inline a parameter, we have to make sure to also inline it in the delay expression and duration.

Note that evaluating the delayed_feedback_function() could still give non-NaN results even if inputs were missing, which made this bug somewhat hard to encounter and track down. The fact that this happens is due to the expand() call; if we would call the original MX function, it would complain about free variables. Why CasADi does not always return NaN for outputs of which not all inputs were specified is unknown though.