connection: do not unregister close callback on close

[vincentbernat]

This is done automatically and if the connection has been closed unexpectedly, this will trigger an error. We ignore the error but it can appear in the logs.

[rgbkrk]

There's not another way to check if it's closed first and then unregister the callback?

[vincentbernat]

In this case, this is not really important as the close callback is always unregistered automatically. However, we have the problem for other kind of callbacks that cannot be unregistered if the connection is closed unexpectedly. I have asked on the libvirt mailing list for some guidance on how to handle all that.