Scenario ending might not be recorded correctly

[duyminh1998]

Describe the bug
Related to issue #25, when a scenario ends in-game, the Scenario has Ended event might not fire properly and the environment might not know that the scenario has ended and get stuck.

To Reproduce
Steps to reproduce the behavior:

1. Load the scen/steam_demo_restart.scen scenario.
2. Disable the Scenario has Ended event.
3. Let the scenario run.
4. See error

Expected behavior
We need to know when the Scenario has Ended event has not fired properly and handle it accordingly. Currently, we can also use the CMOEnv::end_game() function to end the game.