System3: Fix Y 4 1 (random) to return 1

Gakuen KING's original implementation returns 1 for num=1; it returns 0
only when num is 0.

The line dates back to the initial upstream import and had never been
changed. nact_sys1.cpp and nact_sys2.cpp still have the same expression
but they are left alone.

src/sys/nact_sys3.cpp

@@ -713,7 +713,7 @@ void NACT_Sys3::exec_y(int cmd, int param)
 			}
 			break;
 		case 4:
-			RND = (param == 0 || param == 1) ? 0 : random(param);
+			RND = param == 0 ? 0 : random(param);
 			break;
 		case 5:
 			break;