Fix call to getRouter()

Without this the PHP error log gets filled with:

```
[Tue Apr 15 20:16:54 2014] [error] [client 192.168.122.29] PHP Fatal error:  Call to undefined method OC::getRouter() in /var/www/core/apps-external/search_lucene/lib/lucene.php on line 289
```
Merge pull request #24 from owncloud/fix-ro

Fix call to getRouter()