Currently when a category is deleted, if it has an associated chat
channel, the latter won’t be deleted automatically.
The fix is quite simple as we were simply missing a `dependent:
:destroy` option on the existing relation.
Currently it’s not possible to delete a category if an associated chat
channel is present even if there are no messages in this channel.
This can lead to annoying situations for our users.
This patch addresses the issue by checking if the channel is empty
instead of just checking if there is a channel.