fix g.cubes eating green slime

Back when dead green slime left a corpse, gelatinous cubes wouldn't
eat that, but they would eat globs of green slime without being
affected.  Add the missing glob check so g.cubes will engulf globs
of green slime instead of eating those.

src/mon.c

@@ -929,7 +929,8 @@ struct monst *mtmp;
                        || otmp->otyp == RIN_SLOW_DIGESTION)
                    /* cockatrice corpses handled above; this
                       touch_petrifies() check catches eggs */
-                   || ((otmp->otyp == CORPSE || otmp->otyp == EGG)
+                   || ((otmp->otyp == CORPSE || otmp->otyp == EGG
+                        || otmp->globby)
                        && ((touch_petrifies(&mons[otmp->corpsenm])
                             && !resists_ston(mtmp))
                            || (otmp->corpsenm == PM_GREEN_SLIME