Only call xptone_complete() if there's foreground notes

Otherwise there's a race condition that will crash Win32 at least.
Fixes ticket 199.

src/conio/cterm.c

@@ -902,12 +902,14 @@ static void play_music(struct cterminal *cterm)
 	}
 	cterm->music=0;
 	cterm->musicbuf[0]=0;
+	if (fore_count) {
 		while(fore_count) {
 			sem_wait(&cterm->note_completed_sem);
 			fore_count--;
 		}
 		xptone_complete();
 	}
+}
 
 void
 cterm_clreol(struct cterminal *cterm)