avahi-test: do reverse lookups only when the corresponding lookups succeed

[evverx]

Fixes

+ valgrind --track-origins=yes --exit-on-first-error=yes --error-exitcode=1 --leak-check=full --track-fds=yes /tmp/tmp.4MDJpCvVh1/avahi-test ipv6.local
==62957== Memcheck, a memory error detector
==62957== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==62957== Using Valgrind-3.22.0 and LibVEX; rerun with -h for copyright info
==62957== Command: /tmp/tmp.4MDJpCvVh1/avahi-test ipv6.local
==62957==
==62957== Use of uninitialised value of size 8
==62957==    at 0x48C60BB: _itoa_word (_itoa.c:183)
==62957==    by 0x48D0C9B: __printf_buffer (vfprintf-process-arg.c:155)
==62957==    by 0x48EF991: __vsprintf_internal (iovsprintf.c:62)
==62957==    by 0x499EE9E: __sprintf_chk (sprintf_chk.c:40)
==62957==    by 0x49AACA9: sprintf (stdio2.h:30)
==62957==    by 0x49AACA9: inet_ntop4 (inet_ntop.c:85)
==62957==    by 0x49AACA9: inet_ntop (inet_ntop.c:57)
==62957==    by 0x10A91F: avahi_resolve_address_with_socket (avahi.c:138)
==62957==    by 0x10AB11: avahi_resolve_address (avahi.c:181)
==62957==    by 0x10B85F: main (avahi-test.c:38)
==62957==  Uninitialised value was created by a stack allocation
==62957==    at 0x10B780: main (avahi-test.c:26)
==62957==
==62957==
==62957== Exit program on first error (--exit-on-first-error=yes)

Closes #104

[evverx]

The CI here is useless. I'll merge it once https://github.com/evverx/avahi/actions/runs/19606501739/job/56146109229?pr=3 is green and then start running the test under Valgrind in the avahi repository.