Fixed wildcard encoding issue for QP

[nick-bachmann]

The following viper program should not verify. The assert statement should fail since the permission amounts on location x.f and y.f might have totally different positive permission amounts according to my understanding of the wildcard keyword.

field f: Int

method main(s: Set[Ref])
{
inhale forall r:Ref :: {r in s } r in s ==> acc(r.f, wildcard)

var x: Ref
var y: Ref

assume x in s 
assume y in s
assume x != y

//:: ExpectedOutput(assert.failed:assertion.false)
assert perm(x.f) == perm(y.f)

}