only HTTPError (inherit from ULRError) has read and headers attributes

Author: Mathieu

shotgun_api3/shotgun.py

@@ -2689,7 +2689,7 @@ def download_attachment(self, attachment=False, file_path=None, attachment_id=No
                 attachment = req.read()
         # 400 [sg] Attachment id doesn't exist or is a local file
         # 403 [s3] link is invalid
-        except urllib.error.URLError as e:
+        except urllib.error.HTTPError as e:
             if file_path:
                 fp.close()
             err = f"Failed to open {url}\n{e}"