eliminate gcc 13.2.0 warnings that recently appeared

timeout.c:550:1: warning: no previous prototype for ‘region_dialogue’ [-Wmissing-prototypes]
  550 | region_dialogue(void)
      | ^~~~~~~~~~~~~~~

../win/curses/curswins.c: In function ‘curses_destroy_win’:
../win/curses/curswins.c:202:33: warning: variable ‘dummyht’ set but not used [-Wunused-but-set-variable]
  202 |     int mapwidth = 0, winwidth, dummyht;
      |                                 ^~~~~~~

src/timeout.c

@@ -14,6 +14,7 @@ staticfn void slime_dialogue(void);
 staticfn void slimed_to_death(struct kinfo *) NO_NNARGS;
 staticfn void sickness_dialogue(void);
 staticfn void phaze_dialogue(void);
+staticfn void region_dialogue(void);
 staticfn void done_timeout(int, int);
 staticfn void slip_or_trip(void);
 staticfn void see_lamp_flicker(struct obj *, const char *) NONNULLPTRS;

win/curses/curswins.c

@@ -224,6 +224,7 @@ curses_destroy_win(WINDOW *win)
     if (win == activemenu)
         activemenu = NULL;
     curses_refresh_nethack_windows();
+    nhUse(dummyht);
 }