* FIX: Link notification to first unread post
If a topic with a few posts was posted in a watched category or with a
watched tag, the created notification would always point to the last
post, instead of pointing to the first one.
The root cause is that the query that fetched the first unread post
uses 'TopicUser' records and those are not created by default for
user watching a category or tag. In this case, it should use the
'CategoryUser' or 'TagUser' records.
* DEV: Use named bind variables
d1d9f83304