Crash when "submission_finished" not sent by the scheduler

(Outdated)Flow of events:

• Scheduler sends "call_me_later" for the time 100
• All jobs have finished at time 50
• The "call_me_later" event is kind of forgotten by Batsim and the simulation_ends event is sent to the scheduler, causing the simulation to stop.

I think that it simply lacks a condition in is_simulation_finished (server.cpp) with a count on the number of "call_me_later requests" and "requested_call" (or just count the number of "sleeper" processes).