Update config/dansguardian/dansguardian.php

Added return code check when fetching the blacklists. In the previous version, the blacklist directories were removed if the fetch failed. Once the directories were removed, dansguardian would not start because the config files referenced blacklist files that did not exist. This version does not remove the blacklist directories if the blacklist fetch fails.
Merge pull request #332 from rjcrowder/master

Fix to not remove blacklists if the fetch fails