cubicweb #784780 [sessions] crash on long transaction when operating as anonymous [resolved]

anonymous sessions are short lived if the current transaction exceeds it, one can see things such as:

Traceback (most recent call last):
 File "/home/auc/src/fcw/cubicweb/server/repository.py", line 636, in commit
   return self._get_session(sessionid).commit()
 File "/home/auc/src/fcw/cubicweb/server/session.py", line 717, in commit
   self.reset_pool(ignoremode=True)
 File "/home/auc/src/fcw/cubicweb/server/session.py", line 106, in __exit__
   self.session.set_read_security(self.oldread)
 File "/home/auc/src/fcw/cubicweb/server/session.py", line 338, in set_read_security
   oldmode = self.read_security
 File "/home/auc/src/fcw/cubicweb/server/session.py", line 328, in read_security
   self._threaddata.read_security = self.DEFAULT_SECURITY
AttributeError: 'Session' object has no attribute '_threaddata'
prioritynormal
typebug
done in3.8.5
load0.500
load left0.000
closed by<not specified>