Remove unnecessary clamping

Author: reivilibre

synapse/storage/databases/main/thread_subscriptions.py

@@ -133,17 +133,14 @@ def _should_skip_autosubscription_after_unsubscription(
         # For normal rooms, these two orderings should be positive, because
         # they don't refer to a specific event but rather the maximum at the
         # time of unsubscription.
+        #
         # However, for rooms that have never been joined and that are being peeked at,
         # we might not have a single non-backfilled event and therefore the stream
-        # ordering might be negative.
-        # In this case, we clamp it at zero and ensure we fall back to
-        # using topological ordering.
-        unsubscribed_at = attr.evolve(
-            unsubscribed_at, stream=max(0, unsubscribed_at.stream)
-        )
+        # ordering might be negative, so we don't assert this case.
         assert unsubscribed_at.topological > 0
 
-        if unsubscribed_at.stream >= autosub.stream > 0:
+        unsubscribed_at_backfilled = unsubscribed_at.stream < 0
+        if unsubscribed_at_backfilled and unsubscribed_at.stream >= autosub.stream > 0:
             # non-backfilled events: the unsubscription is later according to
             # the stream
             return True