- garbage collect static event handlers on restart

Remaining object(s) led to a potential crash on the next garbage collection cycle
Assertion failure was triggered during restarting in Debug configuration

(cherry picked from commit e085a8d58a)

src/d_main.cpp

@@ -2779,6 +2779,7 @@ void D_DoomMain (void)
 		ST_Clear();
 		D_ErrorCleanup ();
 		DThinker::DestroyThinkersInList(STAT_STATIC);
+		E_Shutdown(false);
 		P_FreeLevelData();
 		P_FreeExtraLevelData();