Prevent from saving a non-existing skin path in user prefs

CHANGELOG

@@ -1,6 +1,7 @@
 CHANGELOG RoundCube Webmail
 ===========================
 
+- Prevent from saving a non-existing skin path in user prefs (#1486936)
 - Improve handling of single-part messages with bogus BODYSTRUCTURE (#1486898)
 - Fix path to SQL files when using pgsql/mysqli/sqlsrv drivers (#1486902)
 - Fix upgrade script for SQLite (#1486903)

program/include/rcube_template.php

@@ -138,13 +138,21 @@ class rcube_template extends rcube_html_page
      */
     public function set_skin($skin)
     {
-        if (!empty($skin) && is_dir('skins/'.$skin) && is_readable('skins/'.$skin))
+        $valid = false;
+        
+        if (!empty($skin) && is_dir('skins/'.$skin) && is_readable('skins/'.$skin)) {
             $skin_path = 'skins/'.$skin;
-        else
+            $valid = true;
+        }
+        else {
             $skin_path = $this->config['skin_path'] ? $this->config['skin_path'] : 'skins/default';
+            $valid = !$skin;
+        }
 
         $this->app->config->set('skin_path', $skin_path);
         $this->config['skin_path'] = $skin_path;
+        
+        return $valid;
     }
 
     /**

program/steps/mail/show.inc

@@ -29,7 +29,7 @@ if ($uid = get_input_value('_uid', RCUBE_INPUT_GET)) {
   if (empty($MESSAGE->headers)) {
     rcmail_message_error($uid);
   }
-
+sleep(5);
   send_nocacheing_headers();
 
   $mbox_name = $IMAP->get_mailbox_name();

program/steps/settings/save_prefs.inc

@@ -116,8 +116,9 @@ switch ($CURR_SECTION)
       $OUTPUT->command('reload', 500);
     }
 
-    // switch skin
-    $OUTPUT->set_skin($a_user_prefs['skin']);
+    // switch skin (if valid, otherwise unset the pref and fall back to default)
+    if (!$OUTPUT->set_skin($a_user_prefs['skin']))
+      unset($a_user_prefs['skin']);
 
     // force min size
     if ($a_user_prefs['pagesize'] < 1)