Fix loghandler memleak

[iekashaev]

Fixed potential memleak, when using dynamic polymorphism.

For all base classes we need to use virtual destructor.

I attach example to reproduce the memleak:

class TestLogHandler : public ILogHandler {
  public:
    void log(std::string message, LogLevel level) override {
      // some log logic
    }
};

int main() {
  ILogHandler* handler = new TestLogHandler();
  delete handler;
  return 0;
}

Thanks!

[kiner-shah]

Nice find.