Fix: samurai splint mails were not always rustproof

Their starting splint mails' material was random, and then set to iron later in u_init. If their original material was inherently fixed, oerodeproof would not be set. A consequence of overzealous use of the new maybe_erodeproof function; revert to the previous code. I also did it for convict iron balls just to be safe, though I imagine those are, y'know, always iron.

Author: saltwaterterrapin

doc/evilhack-changelog.md

@@ -3382,3 +3382,4 @@ The following changes to date are:
 - Fix: spec_applies didn't consider if target was underwater
 - Fix: monster priests shouldn't wield edged weapons either
 - Fix: reactivate offhand weapon intrinsics when catching a returning weapon
+- Fix: samurai splint mails were not always rustproof

src/mkobj.c

@@ -1130,10 +1130,10 @@ boolean artif;
                 && (moves <= 1 || In_quest(&u.uz))) {
 #ifdef UNIXPC
                 /* optimizer bitfield bug */
-                maybe_erodeproof(otmp, 1);
+                otmp->oerodeproof = 1;
                 otmp->rknown = 1;
 #else
-                maybe_erodeproof(otmp, otmp->rknown = 1);
+                otmp->oerodeproof = otmp->rknown = 1;
 #endif
             }
             /* since it's fairly easy for objects to erode/burn
@@ -1143,10 +1143,10 @@ boolean artif;
                 && (moves <= 1)) {
 #ifdef UNIXPC
                 /* optimizer bitfield bug */
-                maybe_erodeproof(otmp, 1);
+                otmp->oerodeproof = 1;
                 otmp->rknown = 1;
 #else
-                maybe_erodeproof(otmp, otmp->rknown = 1);
+                otmp->oerodeproof = otmp->rknown = 1;
 #endif
             }
             break;