service/aoc: Avoid allocating and discarding data

Previously, the code was accumulating data into a std::vector and then
tossing all of it away if a setting was disabled.

Instead, we can just check if it's disabled and do no work at all if
possible. If it's enabled, then we can append to the vector and
allocate.

Unlikely to impact usage much, but it is slightly less sloppy with
resources.