sh/tmpfiles: fix quoting for optional arguments

Some optional arguments were missing quotes in the tests, so produced
spurious warnings.

Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>

sh/tmpfiles.sh.in

@@ -268,10 +268,10 @@ for FILE in $tmpfiles_d ; do
 		age=$6
 		arg=$7
 
-		[ ${4} = '-' ] && uid=0
-		[ ${5} = '-' ] && gid=0
-		[ ${6} = '-' ] && age=0
-		[ ${7} = '-' ] && arg=''
+		[ "${4}" = '-' -o "${4}" = '' ] && uid=0
+		[ "${5}" = '-' -o "${5}" = '' ] && gid=0
+		[ "${6}" = '-' -o "${6}" = '' ] && age=0
+		[ "${7}" = '-' -o "${7}" = '' ] && arg=''
 		set -- "$path" "$mode" "$uid" "$gid" "$age" "$arg"
 
 		[ "$VERBOSE" -eq "1" ] && echo _$cmd "$@"