Smart pointer with local buffer optimization

This is example of smart pointer with type erased deleter and local buffer optimization enabled. It is from the book https://books.google.am/books/about/Hands_On_Design_Patterns_with_C++.html?id=iQGGDwAAQBAJ&printsec=frontcover&source=kp_read_button&redir_esc=y#v=onepage&q&f=false

#include <iostream>

template <typename T>
class smart_ptr
{
    struct deleter_base 
    {
        virtual ~deleter_base() {};
        virtual void apply(T* p) = 0;
    };
    
    template <typename Deleter>
    struct deleter : public deleter_base
    {
        deleter(Deleter d): m_d(d) {}
        void apply(T* p) override 
        {
            m_d(p);
        }
        Deleter m_d;
    };

    deleter_base* m_db;
    T* m_p;
    char m_buf[16];
    
public:
    template <typename Deleter>
    smart_ptr(T* p, Deleter d)
        : m_p(p)
        , m_db( sizeof(Deleter) > sizeof(m_buf) ? new deleter<Deleter>(d) : new (m_buf) deleter<Deleter>(d))
    {
    }
    
    ~smart_ptr() 
    {
        m_db->apply(m_p);
        if (static_cast<void*>(m_db) == static_cast<void*>(m_buf))
        {
            m_db->~deleter_base();
        }
        else 
        {
            delete m_db;
        }
    }
    
    T& operator*() {return *m_p;}
    const T& operator*() const {return *m_p;}
    T* operator->() { return m_p; }
    const T* operator->() const { return m_p; }
};

struct Test 
{
    Test(double d): m_d(d) { std::cout << "Test::Test" << std::endl; }
    ~Test() { std::cout << "Test::~Test" << std::endl; }
    
    double m_d;
};

int main()
{
    auto deleter = [](Test * t) {delete t;};
    smart_ptr<Test> spd(new Test(3.6), deleter);
    
    std::cout << spd->m_d << std::endl;
    
}

One question. When deleter does not fit inside local buffer we allocate memory for it and leave m_buf uninitialized. Is it a bug or I miss something?

In the destructor we compare m_buf which has random value against value returned by new deleter<Deleter>(d). It is not impossible that those values match, right?