Audio focus adjustments

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Don't add directories to the list of files to play

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Fix loop when going to previous and first module is invalid

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Don't attempt to play empty file list

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>