Fix incorrect check for existing files (#150)

Author: frenck

airsonos/rootfs/etc/s6-overlay/s6-rc.d/init-airsonos/run

@@ -8,7 +8,7 @@ declare latency
 
 # Migrate add-on data from the Home Assistant config folder,
 # to the add-on configuration folder.
-if ! bashio::fs.directory_exists '/config/airsonos.xml' \
+if ! bashio::fs.file_exists '/config/airsonos.xml' \
     && bashio::fs.file_exists '/homeassistant/airsonos.xml'; then
     mv /homeassistant/airsonos.xml /config/airsonos.xml \
         || bashio::exit.nok "Failed to migrate AirSonos configuration"