Fixes https://github.com/MusicPlayerDaemon/MPD/discussions/1281

The problem occurred when there was libfmt-dev installed, but it was
too old (e.g. on Debian Buster), and Meson used the wrap fallback.
Those internal MPD libraries where the libfmt dependency was not
declared were still using the old system libfmt headers, which are not
ABI-compatible with MPD's own libfmt build.

libavahi-client uses this one to schedule events immediately.
However, CoarseTimerEvent may be called too late, and cause timeouts.

Fixes broken libavahi-client timeouts.

According to
https://developer.apple.com/documentation/dnssd/1804733-dnsserviceregister
the DNSServiceRef is initialized only if DNSServiceRegister() returns
kDNSServiceErr_NoError.  The faulty error handling code could
therefore crash.