bug#66659: (home-)on-first-login script broken when no gexps are added

[Nils Landt]

Error message:

ice-9/psyntax.scm:2824:12: In procedure syntax-violation:
Syntax error:
/home/nl/.guix-home/on-first-login:3:1233: source expression failed to match 
any pattern in form (when (claim-first-run flag-file-path))

As you can see, there is no body in the "when" expression.

Code in gnu/home/services.scm:438 :

          (if (file-exists? xdg-runtime-dir)
              (when (claim-first-run flag-file-path)
                #$@gexps)

In my case, it appears that gexps is empty, resulting in the invalid syntax.

Broken by b92235ea8b06e304072bad55ae006593ea673568