mxcube.queue de-serialization when no previous queue has been stored

Created by: mguijarr

This is an issue to deal with the problem identified by Peter:

File "/mnt/sync/pkeller/mxcube3/try3/mxcube3/mxcube3/routes/Login.py", line 52, in login
# mxcube.queue = jsonpickle.decode(session.get("queueList", "{}"))

Although jsonpickle.decode(session.get("queueList", "{}")) gives a proper empty dictionary, it prevents MXCuBE to run.

I guess this is because an empty Queue object has to be returned, not an empty dictionary...