castle drawbridge tune tweak

After the drawbridge was destroyed, playing an instrument on the castle
level while knowing the tune continued to offer a chance to play it.
Then nothing interesting happened even if you were close enough to the
former bridge for it to have been useful prior to the destruction.

I think the hero could also be given the tune as a divine prayer boon
after bridge destruction but I didn't verify that.  The player might
not know that the tune is no good anymore, but the hero's patron deity
should.

include/you.h

@@ -1,4 +1,4 @@
-/* NetHack 3.7	you.h	$NHDT-Date: 1686726254 2023/06/14 07:04:14 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.72 $ */
+/* NetHack 3.7	you.h	$NHDT-Date: 1702349061 2023/12/12 02:44:21 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.75 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Robert Patrick Rankin, 2016. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -43,8 +43,8 @@ struct u_event {
     Bitfield(qcalled, 1);      /* called by Quest leader to do task */
     Bitfield(qexpelled, 1);    /* expelled from the Quest dungeon */
     Bitfield(qcompleted, 1);   /* successfully completed Quest task */
-    Bitfield(uheard_tune, 2);  /* 1=know about, 2=heard passtune */
-
+    Bitfield(uheard_tune, 2);  /* 1=know about, 2=heard passtune, 3=bridge has
+                                * been destroyed so tune has become useless */
     Bitfield(uopened_dbridge, 1);   /* opened the drawbridge */
     Bitfield(invoked, 1);           /* invoked Gate to the Sanctum level */
     Bitfield(gehennom_entered, 1);  /* entered Gehennom via Valley */