Sys: Critical sections return false if section is undefined

There is some cases where the fastRestart/mapRestart will clear the critical sections but the VM still runs for 1 frame and tries to enter critical sections eventho the VM is shutdown on the next frame

src/sys/system.c

@@ -99,7 +99,7 @@ void GScr_EnterCriticalSection()
 	}
 	if (!section)
 	{
-		Plugin_Scr_Error(fmt("EnterCriticalSection(): section %s not found.", name));
+		Plugin_Scr_AddBool(qfalse);
 		return;
 	}
 	if (!section->locked)