osx: Fix FileIO::GetLibraryFilename
osx: Fix FileIO::GetLibraryFilename

Was always returning empty path. Fixes failing test and error message when launching an OSX capture from qrenderdoc

baldurk/renderdoc,Zorro666/renderdoc,googlestadia/renderdoc,TurtleRockStudios/renderdoc_public,TurtleRockStudios/renderdoc_public,googlestadia/renderdoc,Zorro666/renderdoc,baldurk/renderdoc,googlestadia/renderdoc,baldurk/renderdoc,Zorro666/renderdoc,googlestadia/renderdoc,TurtleRockStudios/renderdoc_public,TurtleRockStudios/renderdoc_public,baldurk/renderdoc,googlestadia/renderdoc,googlestadia/renderdoc,baldurk/renderdoc,Zorro666/renderdoc,baldurk/renderdoc,TurtleRockStudios/renderdoc_public,Zorro666/renderdoc,Zorro666/renderdoc,TurtleRockStudios/renderdoc_public