drives not present shouldn't lock media server

[gguruusa]

If a removable drive is used to hold content, and that drive is not present when ps3mediaserver starts, ps3mediaserver won't serve any content from any drive.

Additionally, I can't recall if a lock on media directories is held by ps3mediaserver, preventing removal of removable drives without stopping and reconfiguring ps3mediaserver. I imagine solving this is a bigger problem because plugging in a removable drive with content after its removal should re-enable that content.