We want to allow MTBDD engine model checking without having an ODD
to encode the BDD state to index information. This allows to deal
with models where the state space is too big for the ODD index type (2^63).
Here, we harden all the places where the ODD information is accessed
to gracefully handle the abscence of the ODD:
* When trying to convert from MTBDD to explicit vector, a
missing ODD is fatal
* When printing state values or a state list, index information is
not available and thus omitted
* For the hybrid and sparse engine, the odd index checks (whether
the number of states fit into an int32_t) are now done using
helper functions that handle both null ODD and out-of-range values.
Joachim Klein
b49ecc8dcb