Clean up some suspicious code. There's no guarantee a constant of integer type is a ConstantInt, so it's not safe to just cast<> these to ConstantInt. (It could be a constant expression, for example) The code is shorter this way too :).

module bug40;

char[] func(void* p)
{
    return null;
}

void main()
{
    char[] function(void*) fp = &func;
    assert(fp(null) is null);
}