db/limits: Limit SQL query results

[drahnr]

At the RPC level we do have the notion of too_many_entries, however, to come to the decision we already did a full SQL query of i.e. all assets.

Proposal

Limit the SQL queries to N+1 entries, where N is the maximum number we would return without yielding a too_many_entries response to the requester. That way we don't burn CPU cycles on very large assets.