[fantia] prevent '.html' file downloads

gallery_dl/extractor/fantia.py

@@ -56,6 +56,7 @@ class FantiaExtractor(Extractor):
                         "%s#post-content-id-%s", content["visible_status"],
                         post["post_url"], content["id"])
 
+                post["_http_validate"] = self._validate_response
                 for file in files:
                     post.update(file)
                     post["num"] += 1
@@ -90,6 +91,10 @@ class FantiaExtractor(Extractor):
         self.headers["X-CSRF-Token"] = text.extr(
             page, 'name="csrf-token" content="', '"')
 
+    def _validate_response(self, response):
+        return not response.history or not response.headers.get(
+            "content-type", "").startswith("text/html")
+
     def _get_post_data(self, post_id):
         """Fetch and process post data"""
         url = self.root+"/api/v1/posts/"+post_id