When bootstrapping and running as PID 1, /etc/{passwd,shadow} may be unavailable.
Gracefully handle that.

diff --git a/modules/dmd/support.scm b/modules/dmd/support.scm
index 9b592c5..602e409 100644
--- a/modules/dmd/support.scm
+++ b/modules/dmd/support.scm
@@ -151,7 +151,10 @@ There is NO WARRANTY, to the extent permitted by law.")))
 
 
 ;; Home directory of the user.
-(define user-homedir (passwd:dir (getpwuid (getuid))))
+(define user-homedir
+  (or (false-if-exception (passwd:dir (getpwuid (getuid))))
+      (getenv "HOME")
+      "/"))
 
 ;; Logfile.
 (define default-logfile