eeprom.js: check for undefined
eeprom.js: check for undefined

* Per https://github.com/jadonk/bonescript/issues/35

risebox/bonescript,il9ue/bonesimulator,mwillbanks/octalbonescript,jadonk/bonescript,theoctal/octalbonescript,il9ue/bonesimulator,beagleboard/bonescript,beagleboard/bonescript,risebox/bonescript,jadonk/bonescript