message: fix memory leak in MPIOffloadDevice (via ObjectHandle bug)
diff: namespace ospray {
  - static std::map<int64,Ref<ospray::ManagedObject>> objectByHandle;
  + static std::map<int64, ospray::ManagedObject*> objectByHandle;
  static std::stack<int64> freedHandles;
  //! next unassigned ID on this node
  @@ -74,7 +74,7 @@ namespace ospray {
  {
  auto it = objectByHandle.find(i64);
  Assert(it != objectByHandle.end());
  - it->second = nullptr;
  + it->second->refDec();
  objectByHandle.erase(it);
  }
  @@ -112,13 +112,13 @@ namespace ospray {
  #endif
  return nullptr;
  }
  - return it->second.ptr;
  + return it->second;
  }
  ObjectHandle ObjectHandle::lookup(ManagedObject *object)
  {
  for (auto it = objectByHandle.begin(); it != objectByHandle.end(); it++) {
  - if (it->second.ptr == object) return(ObjectHandle(it->first));
  + if (it->second == object) return(ObjectHandle(it->first));
  }
  return(nullHandle);
  