Update index.js

[sansamour]

Fix error: TypeError: Cannot set property 'length' of undefined

[jhiesey]

Thanks!

obj is already set here: https://github.com/sansamour/mp4-box-encoding/blob/9323f264ca3eea19ec065ac3b18a13edc2a6af0a/index.js#L151

Is .decode()returning undefined? If so that's the place to fix it.

[sansamour]

I know you defined it here:

var obj = {}

But i ran code test i saw error:

TypeError: Cannot set property 'length' of undefined

so, i added line:

if(obj == undefined) obj = {}

Code test ran well

I think perhaps this line return undefined

obj = decode(buffer, start, end)

[nklhtv]

this line returns undefined. its not implemented