Fix type inference issues with generic method calls.

[m-carrasco]

Without this fix, the type inference analysis types "b" with !0 rather than int32. That generates a conflict with the Foo's signature.

class A<T>{

public T Get() { ... }
}
                    int Foo(){
                        A<int32> a = new A<int32>();
                        int b = a.Get();
                        return b;
                    }