Fix Retry-After header never parsed on non-2xx responses

requests.Response.__bool__() returns False for non-2xx status codes.
The checks `if e.response` and `if response` evaluated to False for
429 responses, so parse_retry_after() was never called and the SDK
fell back to normal backoff instead of respecting Retry-After.

Changed both checks to explicit `is not None` comparisons.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: MichaelGHSeg

segment/analytics/consumer.py

@@ -78,7 +78,7 @@ def pause(self):
 
     def set_rate_limit_state(self, response):
         """Set rate-limit state from a 429 response with a valid Retry-After header."""
-        retry_after = parse_retry_after(response) if response else None
+        retry_after = parse_retry_after(response) if response is not None else None
         if retry_after is not None:
             self.rate_limited_until = time.time() + retry_after
         if self.rate_limit_start_time is None:
@@ -257,7 +257,7 @@ def calculate_backoff_delay(attempt):
                 # to caller (pipeline blocking). Without Retry-After, fall
                 # through to counted backoff like any other retryable error.
                 if e.status == 429:
-                    retry_after = parse_retry_after(e.response) if e.response else None
+                    retry_after = parse_retry_after(e.response) if e.response is not None else None
                     if retry_after is not None:
                         self.set_rate_limit_state(e.response)
                         raise