[bugfix] prevent crash when no user id is found

[sanderegg]

What do these changes do?

• prevent following assertion from happening in webserver and logs error instead as this should not be hapenning

message
ERROR:engineio.server:disconnect async handler error
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/engineio/asyncio_server.py", line 410, in _trigger_event
    ret = await self.handlers[event](*args)
  File "/usr/local/lib/python3.6/site-packages/socketio/asyncio_server.py", line 518, in _handle_eio_disconnect
    await self._handle_disconnect(sid, '/')
  File "/usr/local/lib/python3.6/site-packages/socketio/asyncio_server.py", line 423, in _handle_disconnect
    await self._trigger_event('disconnect', '/', sid)
  File "/usr/local/lib/python3.6/site-packages/socketio/asyncio_server.py", line 466, in _trigger_event
    ret = await self.handlers[namespace][event](*args)
  File "/usr/local/lib/python3.6/site-packages/simcore_service_webserver/socketio/handlers_utils.py", line 18, in wrapped
    return await func(*args, **kwargs, app=app)
  File "/usr/local/lib/python3.6/site-packages/simcore_service_webserver/socketio/handlers.py", line 109, in disconnect
    user_id = socketio_session["user_id"]
KeyError: 'user_id'

Related issue number

How to test

Checklist

• Did you change any service's API? Then make sure to bundle document and upgrade version (make openapi-specs, git commit ... and then make version-*)
• Unit tests for the changes exist
• Runs in the swarm
• Documentation reflects the changes
• New module? Add your github username to .github/CODEOWNERS

[codecov]

Codecov Report

Merging #1349 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1349      +/-   ##
==========================================
- Coverage   72.75%   72.73%   -0.02%     
==========================================
  Files         201      201              
  Lines        8356     8358       +2     
  Branches      938      939       +1     
==========================================
  Hits         6079     6079              
- Misses       2004     2005       +1     
- Partials      273      274       +1     

Flag	Coverage Δ
#integrationtests	57.82% <75.00%> (-0.03%)	⬇️
#unittests	67.06% <75.00%> (-0.02%)	⬇️

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