There was two issues with the previous code:
1. It was using a weak heuristic to determine whether the
current thread is a channel (ID is a number)
2. For any channel, it was always passing `moderated_channel_ids`
with some values to the server, even though the channel
is not moderated at all.
This commit solves both issues by passing `moderated_channel_ids`
only for moderated channel. Also, this logic has been moved from
SearchableThread to Channel, since moderation makes only sense for
channels and channels are aware of whether they are moderated or
not.
Alexandre Kühn
d3ceaa3adc