Merge pull request #3962 from wkennington/master.iffix

nixos/utils: Don't remove first character if not a /

nixos/lib/utils.nix

@@ -5,6 +5,7 @@ rec {
   # Escape a path according to the systemd rules, e.g. /dev/xyzzy
   # becomes dev-xyzzy.  FIXME: slow.
   escapeSystemdPath = s:
-   replaceChars ["/" "-" " "] ["-" "\\x2d" "\\x20"] (substring 1 (stringLength s) s);
+   replaceChars ["/" "-" " "] ["-" "\\x2d" "\\x20"]
+    (if hasPrefix "/" s then substring 1 (stringLength s) s else s);
 
 }