What this MR does / why does DuMux need it:
Currently it is possible to set several checkpoints at the same time step. This seems to be a bug, since it yields to a time step size of 0.0, which causes a crash of the Newton solver due to Nan values.
Notes for the reviewer
Is there any use case for several checkPoints at the same time, which I don't consider?
Before you request a review from someone, make sure to revise the following points:
\n character. Make sure there is no
\ No newline at end of file comment in "Changes" of this MR.