优化首帧功能，如果没传入首帧，则提取首帧。

wechat_ipad/client/message.py

@@ -219,7 +219,8 @@ class MessageMixin(WechatAPIClientBase):
         has_image = False
         if not image:
             image = Path(os.path.join(Path(__file__).resolve().parent, "fallback.png"))
-
+        else:
+            has_image = True
         # get video base64 and duration
         if isinstance(video, str):
             vid_base64 = video