Label slot machine ids, fix GetPriceReduction

include/constants/slot_machine.h

@@ -3,4 +3,13 @@
 
 #define SLOT_MACHINE_COUNT 12
 
+// Slot machine IDs
+#define SLOT_MACHINE_UNLUCKIEST 0
+#define SLOT_MACHINE_UNLUCKIER  1
+#define SLOT_MACHINE_UNLUCKY    2
+#define SLOT_MACHINE_LUCKY      3
+#define SLOT_MACHINE_LUCKIER    4
+#define SLOT_MACHINE_LUCKIEST   5
+#define NUM_SLOT_MACHINE_IDS    6
+
 #endif // GUARD_CONSTANTS_SLOT_MACHINE_H