ftp-client: Fix off-by-one when trying addresses in 'ftp-open'.

* guix/ftp-client.scm (ftp-open): Change to use 'match' instead of
car/cdr, and fix off-by-one (was '(null? addresses)' instead of
'(null? (cdr addresses))'.)

guix/ftp-client.scm

@@ -139,8 +139,9 @@ TIMEOUT, an ETIMEDOUT error is raised."
                      AI_ADDRCONFIG)))
 
   (let loop ((addresses addresses))
-    (let* ((ai (car addresses))
-           (s  (socket (addrinfo:fam ai)
+    (match addresses
+      ((ai rest ...)
+       (let ((s (socket (addrinfo:fam ai)
                         ;; TCP/IP only
                         SOCK_STREAM IPPROTO_IP)))
 
@@ -161,9 +162,9 @@ TIMEOUT, an ETIMEDOUT error is raised."
            (lambda args
              ;; Connection failed, so try one of the other addresses.
              (close s)
-          (if (null? addresses)
+             (if (null? rest)
                  (apply throw args)
-              (loop (cdr addresses))))))))
+                 (loop rest)))))))))
 
 (define (ftp-close conn)
   (close (ftp-connection-socket conn)))