window-ports should respect flags.silent setting

Like tty_nhbell() in termcap.c, window-ports really should
respect the flags.silent setting.

doc/window.txt

@@ -617,6 +617,8 @@ E.  Misc. Routines
 make_sound(???) -- To be determined later.  THIS IS CURRENTLY UN-IMPLEMENTED.
 nhbell()	-- Beep at user.  [This will exist at least until sounds are
 		   redone, since sounds aren't attributable to windows anyway.]
+                   Implementation should respect the flags.silent setting just
+                   like the tty window-port does in tty_nhbell().
 mark_synch()	-- Don't go beyond this point in I/O on any channel until
 		   all channels are caught up to here.  Can be an empty call
 		   for the moment

win/Qt/qt_bind.cpp

@@ -628,7 +628,8 @@ int NetHackQtBind::qt_nh_poskey(coordxy *x, coordxy *y, int *mod)
 
 void NetHackQtBind::qt_nhbell()
 {
-    QApplication::beep();
+    if (!::flags.silent)
+        QApplication::beep();
 }
 
 int NetHackQtBind::qt_doprev_message()

win/curses/cursmain.c

@@ -977,7 +977,8 @@ nhbell()        -- Beep at user.  [This will exist at least until sounds are
 void
 curses_nhbell(void)
 {
-    beep();
+    if (!flags.silent)
+        beep();
 }
 
 /*

win/win32/mswproc.c

@@ -1481,12 +1481,13 @@ mswin_nh_poskey(coordxy *x, coordxy *y, int *mod)
 
 /*
 nhbell()        -- Beep at user.  [This will exist at least until sounds are
-                   redone, since sounds aren't attributable to windows
+                   redone, since sounds aren't attributable to windows anyway.]
-anyway.]
 */
 void
 mswin_nhbell(void)
 {
+    /* this currently does nothing, but if that ever changes, the setting
+       of flags.silent should be respected */
     logDebug("mswin_nhbell()\n");
 }