cubicweb-trackervcs #2872501 SearchRevisionTicketOp crash if it finds a bogus eid [validation pending]

if ticket_eid is not an entity...

File "/usr/share/cubicweb/cubes/trackervcs/hooks.py", line 87, in precommit_event
for ticket in tickets(self.session, eids, rev.repository.eid):
File "/usr/share/cubicweb/cubes/trackervcs/hooks.py", line 53, in tickets
project = rset.get_entity(0, 1)
File "/usr/lib/pymodules/python2.6/logilab/common/decorators.py", line 66, in wrapped
return self.__call__(*args, **kwargs)
File "/usr/lib/pymodules/python2.6/logilab/common/decorators.py", line 94, in __call__
_cache[args] = __me.callable(self, *args)
File "/usr/lib/python2.6/dist-packages/cubicweb/rset.py", line 428, in get_entity
etype = self.description[row][col]
IndexError: tuple index out of range