Properly stop game if it can't start due to too few players

Before it would be stuck in a "limbo" where it's still in join phase,
but with a real GameState instead of a PregameState which causes various
issues, such as all subsequent joins raising the player count to 1 and
not actually succeeding.

src/pregame.py

@@ -260,6 +260,7 @@ def _isvalid(mode, allow_vote_only):
                     del defroles[srole]
         if not defroles:
             wrapper.send(messages["no_settings_defined"].format(wrapper.source, lv))
+            stop_game(ingame_state, abort=True, log=False)
             return
         for role, num in defroles.items():
             # if an event defined this role, use that number. Otherwise use the number from ROLE_GUIDE