(svn r2134) Return the correct error message if rail is already under a bridge, fix for r2131

rail_cmd.c

@@ -299,12 +299,13 @@ int32 CmdBuildSingleRail(int x, int y, uint32 flags,
 	switch (GetTileType(tile)) {
 		case MP_TUNNELBRIDGE:
 			if ((m5 & 0xC0) != 0xC0 || // not bridge middle part?
-					(m5 & 0x01 ? 1 : 2) != rail_bit || // wrong direction?
+					(m5 & 0x01 ? 1 : 2) != rail_bit) { // wrong direction?
-					(m5 & 0x38) != 0x00) { // no clear land underneath?
 				// Get detailed error message
 				return DoCommandByTile(tile, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
 			}
 
+			switch (m5 & 0x38) { // what's under the bridge?
+				case 0x00: // clear land
 					ret = CheckRailSlope(tileh, rail_bit, 0, tile);
 					if (ret & CMD_ERROR) return ret;
 					cost += ret;
@@ -317,6 +318,15 @@ int32 CmdBuildSingleRail(int x, int y, uint32 flags,
 					}
 					break;
 
+				case 0x20: // rail already there
+					return_cmd_error(STR_1007_ALREADY_BUILT);
+
+				default:
+					// Get detailed error message
+					return DoCommandByTile(tile, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
+			}
+			break;
+
 		case MP_RAILWAY:
 			if (!CheckTrackCombination(m5, rail_bit, flags) ||
 					!EnsureNoVehicle(tile)) {