Disable CvodeF checkpointing (#2645)

amici wants to avoid sundials' checkpointing, that's we set `steps` (the number of integration steps at which a checkpoint is created) for `CVodeAdjInit` to the maximum number of integration steps (`mxsteps`) for the forward problem.

However, the checkpoint is created at step `steps`, not at step `steps + 1`.

Therefore, if the forward integration takes exactly `mxsteps`, a checkpoint is still created.

This is not a problem per se, but it may trigger segfaults under circumstances not fully understood (-> LLNL/sundials#49).
Although unlikely, it still occasionally crashes long running optimizations.

This change should make sure that checkpointing never occurs.

src/solver_cvodes.cpp

@@ -716,7 +716,7 @@ void CVodeSolver::adjInit() const {
         status = CVodeAdjReInit(solver_memory_.get());
     } else {
         status = CVodeAdjInit(
-            solver_memory_.get(), static_cast<int>(maxsteps_),
+            solver_memory_.get(), static_cast<int>(maxsteps_ + 1),
             static_cast<int>(interp_type_)
         );
         setAdjInitDone();