Add petless conduct

Breaks saves.

src/minion.c

@@ -520,7 +520,17 @@ gain_guardian_angel(void)
              * [Note: this predates mon->mextra which allows a monster
              * to have both emin and edog at the same time.]
              */
-            mtmp->mtame = 10;
+            /* Too nasty for the game to unexpectedly break petless conduct on
+             * the final level of the game. The angel will still appear, but
+             * won't be tamed. */
+            if (u.uconduct.pets) {
+                /* guardian angel -- the one case mtame doesn't
+                 * imply an edog structure, so we don't want to
+                 * call tamedog().
+                 */
+                mtmp->mtame = 10;
+                u.uconduct.pets++;
+            }
             /* for 'hilite_pet'; after making tame, before next message */
             newsym(mtmp->mx, mtmp->my);
             if (!Blind)