fix bug with missing stable file & timestamps

gimme

@@ -585,7 +585,10 @@ _last_mod_timestamp() {
 _file_older_than_secs() {
 	local file="${1}"
 	local age_secs="${2}"
-	((($(date +%s) - $(_last_mod_timestamp "${file}")) > age_secs))
+	local ts
+	# if the file does not exist, we return true, as the cache needs updating
+	ts="$(_last_mod_timestamp "${file}" 2>/dev/null)" || return 0
+	((($(date +%s) - ts) > age_secs))
 }
 
 _assert_version_given() {