emails.backends.mediawiki: improve error handling

bubble up api error responses

Bug: T412427

Author: jsnshrmn

TWLight/emails/backends/mediawiki.py

@@ -53,10 +53,12 @@ def conn(*args, **kwargs):
 def _handle_maxlag(response):
     """A helper method that handles maxlag retries."""
     data = response.json()
-    try:
-        if data["error"]["code"] != "maxlag":
-            return data
-    except KeyError:
+    if "error" in data:
+        error = data["error"]
+        if error["code"] != "maxlag":
+            msg = "{code}: {info}".format(code=error["code"], info=error["info"])
+            raise Exception(msg)
+    else:
         return data
 
     retry_after = float(response.headers.get("Retry-After", 5))