The BLELocalAttribute and BLERemoteAttribute classes implement a rudimentary reference counting mechanism:

int BLELocalAttribute::retain()
{
  _refCount++;

  return _refCount;
}

int BLELocalAttribute::release()
{
  _refCount--;

  return _refCount;
}

However, _refCount is an instance variable so every call to release() on a pointer that was already deleted will try to access freed memory, defeating the purpose of refcounting. A more modern solution would be to replace this with std::shared_ptr, but this pull request provides a minimalistic fix based on making _refCount a static class variable that lives outside the lifecycle of the instance.

I noticed this issue after merging #237.