gather_subscriptions: Avoid extra queries fetching realm objects.

(imported from commit 591083cfaff454b8ce48aacb5da7913b8fe0a38f)

zerver/lib/actions.py

@@ -1452,7 +1452,7 @@ def gather_subscriptions(user_profile):
     stream_ids = [sub.recipient.type_id for sub in subs]
 
     stream_hash = {}
-    for stream in Stream.objects.filter(id__in=stream_ids):
+    for stream in Stream.objects.select_related("realm").filter(id__in=stream_ids):
         stream_hash[stream.id] = stream
 
     subscribed = []