FIX false setting "Audio output interface"

FIX false setting "Audio output interface" on mpd-config page after reboot with active i2smodule.
A i2smodule can not dissapear without useraction, so it should be save to test if i2smodule is set at this point.
Merge pull request #31 from hondagx35/master

FIX false setting "Audio output interface"