Unify unpolyable objects to single define

include/obj.h

@@ -356,6 +356,10 @@ struct obj {
          && !undiscovered_artifact(ART_EYES_OF_THE_OVERWORLD)))
 #define pair_of(o) ((o)->otyp == LENSES || is_gloves(o) || is_boots(o))
 
+#define unpolyable(o) ((o)->otyp == WAN_POLYMORPH \
+                       || (o)->otyp == SPE_POLYMORPH \
+                       || (o)->otyp == POT_POLYMORPH)
+
 /* achievement tracking; 3.6.x did this differently */
 #define is_mines_prize(o) ((o)->o_id == g.context.achieveo.mines_prize_oid)
 #define is_soko_prize(o) ((o)->o_id == g.context.achieveo.soko_prize_oid)

src/potion.c

@@ -1978,7 +1978,7 @@ dodip()
     } else if (obj->otyp == POT_POLYMORPH || potion->otyp == POT_POLYMORPH) {
         /* some objects can't be polymorphed */
         if (obj->otyp == potion->otyp /* both POT_POLY */
-            || obj->otyp == WAN_POLYMORPH || obj->otyp == SPE_POLYMORPH
+            || unpolyable(obj)
             || obj == uball || obj == uskin
             || obj_resists(obj->otyp == POT_POLYMORPH ? potion : obj,
                            5, 95)) {

src/zap.c

@@ -1964,8 +1964,7 @@ struct obj *obj, *otmp;
         switch (otmp->otyp) {
         case WAN_POLYMORPH:
         case SPE_POLYMORPH:
-            if (obj->otyp == WAN_POLYMORPH || obj->otyp == SPE_POLYMORPH
+            if (unpolyable(obj) || obj_resists(obj, 5, 95)) {
-                || obj->otyp == POT_POLYMORPH || obj_resists(obj, 5, 95)) {
                 res = 0;
                 break;
             }