Fix pet polyed to long worm staying leashed

Long worms cannot be leashed, but polymorphing a leashed pet
into a long worm kept it leashed.

doc/fixes36.3

@@ -210,6 +210,7 @@ parsing for the argument to 'scores' option was sloppy; "3a/o" (slash) and
 wizmakemap could leave genocided monsters on map
 when entering Astral level, initial rendering of guardian angel didn't show
 	it as tame; noticeable if the level was entered with 'hilite_pet' On
+fix a leashed pet polymorphed into a long worm staying leashed
 
 
 Fixes to Post-3.6.2 Problems that Were Exposed Via git Repository

include/extern.h

@@ -38,6 +38,7 @@ E int NDECL(number_leashed);
 E void FDECL(o_unleash, (struct obj *));
 E void FDECL(m_unleash, (struct monst *, BOOLEAN_P));
 E void NDECL(unleash_all);
+E boolean FDECL(leashable, (struct monst *));
 E boolean NDECL(next_to_u);
 E struct obj *FDECL(get_mleash, (struct monst *));
 E const char *NDECL(beautiful);

src/apply.c

@@ -595,7 +595,7 @@ unleash_all()
  *  This ought to exclude various other things, such as lights and gas
  *  spore, is_whirly() critters, ethereal creatures, possibly others.
  */
-static boolean
+boolean
 leashable(mtmp)
 struct monst *mtmp;
 {

src/mon.c

@@ -3762,6 +3762,9 @@ boolean msg;      /* "The oldmon turns into a newmon!" */
     /* take on the new form... */
     set_mon_data(mtmp, mdat);
 
+    if (!leashable(mtmp))
+        m_unleash(mtmp, TRUE);
+
     if (emits_light(olddata) != emits_light(mtmp->data)) {
         /* used to give light, now doesn't, or vice versa,
            or light's range has changed */