Add a default for retry after (#371)

* Add a default for retry after
Signed-off-by: Ben Cassell <ben.cassell@databricks.com>

* Applied black formatter
Signed-off-by: Ben Cassell <ben.cassell@databricks.com>

src/databricks/sql/thrift_backend.py

@@ -353,8 +353,8 @@ def extract_retry_delay(attempt):
             # encapsulate retry checks, returns None || delay-in-secs
             # Retry IFF 429/503 code + Retry-After header set
             http_code = getattr(self._transport, "code", None)
-            retry_after = getattr(self._transport, "headers", {}).get("Retry-After")
-            if http_code in [429, 503] and retry_after:
+            retry_after = getattr(self._transport, "headers", {}).get("Retry-After", 1)
+            if http_code in [429, 503]:
                 # bound delay (seconds) by [min_delay*1.5^(attempt-1), max_delay]
                 return bound_retry_delay(attempt, int(retry_after))
             return None