[BUG] removing calls to monitors.unfreeze() in fine grained propagators may lead to error

[cprudhom]

Describe the bug
In older versions, a call to unfreeze() was required as last instructions of propagate(int).
Choco-solver-4.10.7 removes the requirement of freezing/unfreezing delta monitors (see 84a3fc3), and consequently removes this apparently useless calls.

However, skipping this call may produce over-filtering.

To Reproduce
Not easy to do, but with 3 propagators, p1, p2 and p3 where p1 removes value 1 from variable x, p2 being fine grained and p3 removes another value, say 2, from x, then p2 is scheduled and propagated on fine event (removal of 2) but 1 is also iterated on the call to forEachRemVal.
In many cases, that may have no effect, but if the propagator considers that it is only receiving values that have been deleted since it last woke up (without any safeguards), then there may be a problem.

Environment (please complete the following information):

• Choco-solver version: 4.10.7