Nested super constructor calls crash Nagini

[marcoeilers]

Found by @edgarsvitolins, the following program crashes Nagini (by crashing Viper):

from nagini_contracts.contracts import *

class Grandparent:
    def __init__(self) -> None:
        self.x = 1
        Ensures(Acc(self.x))
        Ensures(self.x == 1)


class Parent(Grandparent):
    def __init__(self) -> None:
        super().__init__()
        Ensures(Acc(self.x))
        Ensures(self.x == 1)


class Child(Parent):
    def __init__(self) -> None:
        super().__init__()
        Ensures(Acc(self.x))
        Ensures(self.x == 1)


def main() -> None:
    c = Child()
    Assert(c.x == 1)


if __name__ == "__main__":
    main()