fix ctypes import for unix

cbz/player.py

@@ -4,9 +4,13 @@ import tkinter as tk
 from io import BytesIO
 from tkinter import ttk
 from tkinter.constants import DISABLED, NORMAL
-from ctypes import windll
 from pathlib import Path
 
+try:
+    from ctypes import windll
+except ImportError:
+    windll = None  # windll is not available on this platform
+
 from PIL import Image, ImageTk
 
 from cbz.comic import ComicInfo