fix memory leak for knight's starting pony

makemon() has a 1% chance to bestow a worn saddle when creating any
rideable monster.  If that chance kicked in on a knight's starting
pony, an extra saddle would end up being created but not worn nor
in inventory nor on floor so not be freed when the game ended.

That 1% chance also overrode saddle suppression for pauper knights.
There wouldn't be any extra saddle but their pony could start with
one, against intent.

Have makedog() (which is only used for starting pet) tell makemon()
to suppress inventory when creating the initial pet.

src/dog.c

@@ -217,7 +217,12 @@ makedog(void)
             petname = "Sirius"; /* Orion's dog */
     }
 
-    mtmp = makemon(&mons[pettype], u.ux, u.uy, MM_EDOG);
+    /* specifying NO_MINVENT prevents makemon() from having a 1% chance
+       of creating a pony with an already worn saddle; dogs and cats
+       aren't affected because they don't have any initial inventory
+       [if anybody adds stranger pets that are expected to have such,
+       they'll need to modify this] */
+    mtmp = makemon(&mons[pettype], u.ux, u.uy, MM_EDOG | NO_MINVENT);
 
     if (!mtmp)
         return ((struct monst *) 0); /* pets were genocided [how?] */
@@ -225,7 +230,7 @@ makedog(void)
     if (!svc.context.startingpet_mid) {
         svc.context.startingpet_mid = mtmp->m_id;
         if (!u.uroleplay.pauper) {
-            /* initial horses already wear saddle (unless hero is a pauper) */
+            /* initial horses start wearing a saddle (pauper hero excluded) */
             if (pettype == PM_PONY
                 && (otmp = mksobj(SADDLE, TRUE, FALSE)) != 0) {
                 /* pseudo initial inventory; saddle is not actually in hero's