Android: Large file read error

When you read file by somethig like
```
var reader = new FileReader();
reader.onloadend=console.log;
reader.readAsText(file);
```
and if the file is bigger that CHUNK_SIZE (256kB) it gives you corrupted file: for example reading file that has about 0.5MB i get string, which length is over 800 000 characters (tested on android).

My solution, in **www/FileReader.js** instead of line
`readSuccessCallback.bind(this, readType, encoding, offset, totalSize, accumulate),`
put
`readSuccessCallback.bind(this, readType, encoding, offset, Math.min(totalSize - this._progress, CHUNK_SIZE), accumulate),`

Start in www/FileReader.js at the readSuccessCallback.bind call, then reproduce the issue on Android with FileReader.readAsText and a file larger than CHUNK_SIZE. Verify that a roughly 0.5MB file is returned without corruption and that smaller files still behave correctly.

Written by the indexing model from the issue text.