Earlier, followed topics in muted streams were not listed in
the 'Recent conversations' table when 'Include muted' filter is
unchecked.
They should be listed as we currently list unmuted topics.
The "test_filter_all" includes tests for muted and not muted topics,
but the 'is_spectator' field is set to 'true'.
Logically, it is incorrect because a topic can't have a
visibility policy set in spectator view.
This commit fixes the incorrect behavior and adds a separate test
for the case 'is_spectator=true'.
The issue was introduced in d0a697f.
narrow is a term that is intended to only apply to a message feed
view; it comes from "narrowing the set of messages you're looking
at from the All messages" so switching it to something different
makes sense.