fix(firestore): BulkWriter pop from an empty deque

Fixes #16138

Author: daniel-sanche

packages/google-cloud-firestore/google/cloud/firestore_v1/bulk_writer.py

@@ -508,8 +508,9 @@ def _schedule_ready_retries(self) -> None:
         )
 
         for _ in range(take_until_index):
-            retry: OperationRetry = self._retries.popleft()
-            retry.retry(self)
+            if self._retries:
+                retry: OperationRetry = self._retries.popleft()
+                retry.retry(self)
         return None
 
     def _request_send(self, batch_size: int) -> bool: