bug#63982: Shepherd can crash when a user service fails to start

[nils]

> Ludovic Courtès <ludo@gnu.org> hat am 22.06.2023 22:08 CEST geschrieben:
> This suggests a problem in the config file: one of the shepherd-*.scm
> files listed above ends up calling (string-append #f …).
> 
> We’d need to see those files to understand what’s happening but it looks
> different from what Maxim reported.

Indeed I misdiagnosed the issue because it happened after a guix upgrade.
I used $XDG_LOG_HOME in my shepherd services, and as of 
f74df2ab879fc5457982bbc85b7455a90e82317d this is no longer set by default. 
Thanks for your help!