Result of `zdd.max_ilevel_cut(...)` may exclude false edge, if operator shortcuts on `false`

[SSoelvsten]

Currently, the max_1level_cut and max_2level_cut functions for the zdd class adds an extra edge to account for edges being paired with the suppressed edge to false. Yet, specifically for the zdd_intsec operation where such a pairing never happens (as it is shortcut by the operator). Hence, we may leave out that edge from the upper bound.