Revert "Remove unneeded DISTINCT from list short URLs query"

[acelaya]

Reverts #2117

The DISTINCT is actually needed, but there's no test covering the combination in which it is.

When filtering short URLs by tags or by search term, the query needs to join with the tags table, in which case the results are not correct without the DISTINCT.

The right fix here would be something in the lines of:

1. Dynamically add DISTINCT only when strictly needed, to reduce the performance impact in some cases at least.
2. Change the way filtering by tag or by search term works. Perhaps using a subquery would work here, but that can introduce its own performance issues and also needs to be tested.

A test covering this case needs to be added.