[WebProfilerBundle] Fix lack of padding in some WDT boxes (e.g. You are not authenticated.)

Fixes bug introduced by https://github.com/symfony/symfony/pull/6615

Before:
![wdt-padding-before](https://f.cloud.github.com/assets/363540/73453/c6779f30-6044-11e2-9df5-682c822ac13c.png)

After:
![wdt-padding-after](https://f.cloud.github.com/assets/363540/73455/cbeaa44e-6044-11e2-9d9b-9184b1351554.png)