[gimp] app: only show a "Last checked" date when we did at least 1 check.

[Jehan <jehanp src gnome org>]

commit ed778303813d07ac1eac4dfbcaa4ed86c5f12f1d
Author: Jehan <jehan girinstud io>
Date:   Tue Feb 11 21:12:42 2020 +0100

    app: only show a "Last checked" date when we did at least 1 check.
    
    If for instance you've got no internet connection or other reasons that
    a check might fail, the check-update-timestamp will be 0, which is
    1970-01-01.
    Thanks to Alexandre Prokoudine for noticing it!

 app/dialogs/about-dialog.c | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)
---
diff --git a/app/dialogs/about-dialog.c b/app/dialogs/about-dialog.c
index 6243996bbe..2b17741221 100644
--- a/app/dialogs/about-dialog.c
+++ b/app/dialogs/about-dialog.c
@@ -268,8 +268,6 @@ about_dialog_add_update (GimpAboutDialog *dialog,
   GDateTime *datetime;
   gchar     *date;
   gchar     *text;
-  gchar     *text2;
-
 
   /* Get the dialog vbox. */
   container = gtk_dialog_get_content_area (GTK_DIALOG (dialog->dialog));
@@ -349,19 +347,28 @@ about_dialog_add_update (GimpAboutDialog *dialog,
   /* Show a check update button. */
   gtk_box_reorder_child (GTK_BOX (vbox), frame, 4);
 
-  datetime = g_date_time_new_from_unix_local (config->check_update_timestamp);
-  date = g_date_time_format (datetime, "%x");
-  text2 = g_strdup_printf (_("Last checked on %s"), date);
-  text = g_strdup_printf ("%s\n<i>%s</i>",
-                          _("Check for updates"), text2);
+  if (config->check_update_timestamp > 0)
+    {
+      gchar *subtext;
+
+      datetime = g_date_time_new_from_unix_local (config->check_update_timestamp);
+      date = g_date_time_format (datetime, "%x");
+      subtext = g_strdup_printf (_("Last checked on %s"), date);
+      g_date_time_unref (datetime);
+      g_free (date);
+
+      text = g_strdup_printf ("%s\n<i>%s</i>",
+                              _("Check for updates"), subtext);
+      g_free (subtext);
+    }
+  else
+    {
+      text = g_strdup_printf ("%s", _("Check for updates"));
+    }
   label = gtk_label_new (NULL);
   gtk_label_set_markup (GTK_LABEL (label), text);
   gtk_label_set_justify (GTK_LABEL (label), GTK_JUSTIFY_CENTER);
-
-  g_date_time_unref (datetime);
-  g_free (date);
   g_free (text);
-  g_free (text2);
 
   button = gtk_button_new ();
   gtk_container_add (GTK_CONTAINER (button), label);