Check if payload contains "committer" info. (GH-31)

There were cases where data["commit"]["committer"] is null.

Author: Mariatta

backport/status_change.py

@@ -17,7 +17,8 @@ async def check_status(event, gh, *args, **kwargs):
     """
     Check the state change
     """
-    if event.data["commit"]["committer"]["login"] == "miss-islington":
+    if event.data["commit"].get("committer") \
+            and event.data["commit"]["committer"]["login"] == "miss-islington":
         sha = event.data["sha"]
         status_url = f"https://api.github.com/repos/python/cpython/commits/{sha}/status"
         request_headers = sansio.create_headers(