guix package: Recover from freshness check transient errors.

* guix/scripts/package.scm (check-package-freshness): Ignore
  `getaddrinfo-error' and `ftp-error' exceptions.

guix/scripts/package.scm

@@ -285,6 +285,9 @@ matching packages."
   "Check whether PACKAGE has a newer version available upstream, and report
 it."
   ;; TODO: Automatically inject the upstream version when desired.
+
+  (catch #t
+    (lambda ()
       (when (gnu-package? package)
         (let ((name      (package-name package))
               (full-name (package-full-name package)))
@@ -298,6 +301,12 @@ but ~a is available upstream~%")
                        (location->string (package-location package))
                        full-name latest-version)))
             (_ #t)))))
+    (lambda (key . args)
+      ;; Silently ignore networking errors rather than preventing
+      ;; installation.
+      (case key
+        ((getaddrinfo-error ftp-error) #f)
+        (else (apply throw key args))))))
 
 
 ;;;