From 2fbb96bfa5cb10baab827b0d71539721f1619324 Mon Sep 17 00:00:00 2001
From: hackykid <hackykid@openttd.org>
Date: Mon, 6 Jun 2005 01:31:36 +0000
Subject: [PATCH] (svn r2415)  - Fix: [newgrf] Powered Wagons - Don't assume an
 undefined callback will fail.

---
 engine.h    | 1 +
 train_cmd.c | 5 +++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/engine.h b/engine.h
index 19ea104922..8a78bec286 100644
--- a/engine.h
+++ b/engine.h
@@ -144,6 +144,7 @@ enum CallbackID {
 // bit positions for rvi->callbackmask, indicates which callbacks are used by an engine
 // (some callbacks are always used, and dont appear here)
 enum CallbackMask {
+	CBM_WAGON_POWER = 0,
 	CBM_REFIT_CAP = 3,
 };
 
diff --git a/train_cmd.c b/train_cmd.c
index d75f58584f..0096e43b49 100644
--- a/train_cmd.c
+++ b/train_cmd.c
@@ -79,9 +79,10 @@ void TrainConsistChanged(Vehicle *v) {
 		// check if its a powered wagon
 		CLRBIT(u->u.rail.flags, VRF_POWEREDWAGON);
 		if ((rvi_v->pow_wag_power != 0) && (rvi_u->flags & RVI_WAGON) && UsesWagonOverride(u)) {
-			uint16 callback;
+			uint16 callback = CALLBACK_FAILED;
 
-			callback = GetCallBackResult(CBID_WAGON_POWER,  u->engine_type, u);
+			if (HASBIT(rvi_u->callbackmask, CBM_WAGON_POWER))
+				callback = GetCallBackResult(CBID_WAGON_POWER,  u->engine_type, u);
 
 			if (callback == CALLBACK_FAILED)
 				callback = rvi_u->visual_effect;