Fix gitea-action user avatar broken on edited menu (#29190) (#29307)

Backport #29190

Fix #29178

models/issues/content_history.go

 	}
 
 	for _, item := range res {
-		item.UserAvatarLink = avatars.GenerateUserAvatarFastLink(item.UserName, 0)
+		if item.UserID > 0 {
+			item.UserAvatarLink = avatars.GenerateUserAvatarFastLink(item.UserName, 0)
+		} else {
+			item.UserAvatarLink = avatars.DefaultAvatarLink()
+		}
 	}
 	return res, nil
 }