With the work on #25500 (reducing CPU client usage), the HS service main loop
callback is enabled as soon as the HS service map changes which happens when
registering a new service.
Unfortunately, for an ephemeral service, we were building the onion address
*after* the registration leading to the "service->onion_address` to be an
empty string.
This broke the "HS_DESC CREATED" event which had no onion address in it. And
also, we were logging an empty onion address for that service.
Fixes#25939
Signed-off-by: David Goulet <dgoulet@torproject.org>
