Minor - download: add response head to log message when json decode fails

download.py

@@ -224,8 +224,9 @@ def get_from_api(url, raise_on_errors=True):
     try:
         content_dict = json.loads(content_str)
     except Exception as e:
+        response_head = content_str[:400]
         log.exception(
-            "API call: {!r}\nException during conversion of API result to json. Result saved to last_api_result.json file.".format(url))
+            "API call: {!r}\nException during conversion of API result to json. Full result saved to last_api_result.json file.\nHere's the head of the answer:".format(url, response_head))
         with open('last_api_result.json', 'wb') as _f:
             _f.write(content_str)
         raise e