Pets will not eat shapeshifter corpses except in extreme circumstances

Ported from SpliceHack, and generalized to all shapeshifters (Splice
only implemented it for chameleons). It's very aggravating when your
powerful but hungry pet chows down on a shapeshifter before you can stop
them and then turns into something much more useless, so this aims to
prevent that.

The extreme circumstances under which a pet will eat a shapeshifter are:
  1. The pet is starving, and prefers polymorph to starvation
  2. The pet's tameness is 1

The reasoning behind the second condition is that if you mistreat your
pet almost to the point of untaming it, it might want to take a chance
on turning into something that might get some more respect from you.
Practically, whenever this happens, this will result in the player now
owning a newly polymorphed and *still* nearly feral pet.

doc/fixes37.0

@@ -113,6 +113,7 @@ add a small chance of surviving food poisoning
 deliberate level teleporter activation ignores magic resistance
 auto-id scroll of remove curse when a known buc-state was changed
 demon lords hate Demonbane
+pets avoid eating shapeshifter corpses unless starving or nearly feral
 
 
 Fixes to 3.7.0-x Problems that Were Exposed Via git Repository

src/dog.c

@@ -807,6 +807,17 @@ register struct obj *obj;
             /* turning into slime is preferable to starvation */
             else if (fptr == &mons[PM_GREEN_SLIME] && !slimeproof(mon->data))
                 return starving ? ACCFOOD : POISON;
+            /* polymorphing is preferable to starvation, and the pet might also
+             * want to take their chances on it if they've been mistreated */
+            else if (is_shapeshifter(fptr)) {
+                if (mon->mtame == 1) {
+                    /* A herbivore still won't eat a nonvegan corpse, but in any
+                     * other circumstance a pet with tameness 1 will happily eat
+                     * a shapeshifter. */
+                    return (herbi && !vegan(fptr)) ? MANFOOD : CADAVER;
+                }
+                return starving ? ACCFOOD : MANFOOD;
+            }
             else if (vegan(fptr))
                 return herbi ? CADAVER : MANFOOD;
             /* most humanoids will avoid cannibalism unless starving;