Splits on ACSL predicates do not try to split and reduce states in which the
predicate is already satisfied or refuted.

A split has failed if the reduced state is equal to the entry state _and_
the predicate evaluates to Unknown.
If the predicate evaluates to True/False in the entry state, then the state
cannot be reduced: the reduced state is then equal to the entry state), but
this is not a failure: the split holds.

When -eva-octagon-through-calls is enabled, fixes a crash on non-integer
formal parameters, on which no relation can be inferred.