Destruction order of `Link` and `ObjectHandle` of `Node`

[FlyingSamson]

Currently the API enables us within a function to open a file, open some group within that file and return the group.
Let's say we have

auto f() -> hdf5::node::Group;

The file will correctly be kept open through the RAII-object chain Group having a Link having a File. So far so good.

However, on destruction of that group returned from the file, I obtain the following error

Failed ~ObjectHandle:
 ObjectHandle: could not close hid= 72057594037927939 type=FILE

The reason for this is that when at the end of a scope like this

{
  auto group = f();
}

group goes out of scope, its base, Node, will destroy its members in reverse order. Thus, first the Link link_ object is tried to be destroyed. This in turn tries to destroy the file. Which fails because there is still the open Group object from that file.

I would therefore propose to reverse the lines in Node

    ObjectHandle handle_; //!< access handle to the object
    Link link_;           //!< stores the link to the object

to read

    Link link_;           //!< stores the link to the object
    ObjectHandle handle_; //!< access handle to the object

If you find this acceptable I can make a MR for this change.

[jkotan]

@FlyingSamson , Thank you for the ticket. Please create the MR.