buddy list: Initialize g_autofree() vars

Othewise a free leads to a crash.
3 jobs for g_auto-crash in 4 minutes and 20 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
passed build-debian-gcc #82824
librem5

00:01:21

 
  Test
passed test:debian-gcc #82825
librem5

00:01:19

 
  Package
passed build-debian-package #82826
librem5

00:01:40