Merge pull request #52 in ZP/z-push from bugfix/ZP-651-wp-does-not-set-http_user_agent to develop

* commit '20281136':
  ZP-651 Only contact DeviceManager if DeviceID is set. Released under the Affero GNU General Public License (AGPL) version 3.

src/backend/zarafa/zarafa.php

@@ -166,7 +166,7 @@ class BackendZarafa implements IBackend, ISearchProvider {
                 // send Z-Push version and user agent to ZCP - ZP-589
                 if (Utils::CheckMapiExtVersion('7.2.0')) {
                     $zpush_version = 'Z-Push_' . @constant('ZPUSH_VERSION');
-                    $user_agent = ZPush::GetDeviceManager()->GetUserAgent();
+                    $user_agent = (Request::GetDeviceID()) ? ZPush::GetDeviceManager()->GetUserAgent() : "unknown";
                     $this->session = @mapi_logon_zarafa($user, $pass, MAPI_SERVER, null, null, 0, $zpush_version, $user_agent);
                 }
                 else {