Add railtype/signal variable to get signal side

src/newgrf_railtype.cpp

@@ -36,6 +36,7 @@
 			case 0x44: return HZB_TOWN_EDGE;
 			case A2VRI_RAILTYPE_SIGNAL_RESTRICTION_INFO: return 0;
 			case A2VRI_RAILTYPE_SIGNAL_CONTEXT: return this->signal_context;
+			case A2VRI_RAILTYPE_SIGNAL_SIDE: return GetNewSignalsSideVariable();
 		}
 	}
 
@@ -59,6 +60,8 @@
 			return GetNewSignalsRestrictedSignalsInfo(this->prog, this->tile, 0);
 		case A2VRI_RAILTYPE_SIGNAL_CONTEXT:
 			return GetNewSignalsSignalContext(this->signal_context, this->tile);
+		case A2VRI_RAILTYPE_SIGNAL_SIDE:
+			return GetNewSignalsSideVariable();
 	}
 
 	DEBUG(grf, 1, "Unhandled rail type tile variable 0x%X", variable);