[TIMOB-7996] Ti API: Stream.writeStream--different handling for end of stream

If writeStream(inputStream, outputStream, chunkSize, callback) is invoked when the input stream is at end of stream, behavior varies by platform. Neither platform appears to follow the spec. From my reading of the spec, it's not clear what's supposed to happen. For the pump callback it specifically says that the bytesProcessed property in the callback arg is set to -1 on end of stream. On iOS, an exception is thrown, so the callback isn't invoked. On Android, bytesProcessed is set to 0 in the callback, errorState is 0, and errorDescription is "". It seems like it would be more consistent with other functionality if bytesProcessed reported -1 in both cases. Same behavior holds for the synchronous version of the method--returns 0 on Android, throws an exception on iOS. If we regard passing an empty stream (or a stream at EOF) as an error, we should treat it as an error on both platforms. Testcase:

var win1 = Titanium.UI.createWindow({  
    title:'Tab 1',
    backgroundColor:'#fff'
});
win1.open();

var stream1 = Ti.Stream.createStream({ 
	source: Ti.createBuffer({ length: 0}),
	mode: Ti.Stream.MODE_READ
});

var stream2 = Ti.Stream.createStream({ 
	source: Ti.createBuffer({ length: 1024}),
	mode: Ti.Stream.MODE_READ
});

Ti.Stream.writeStream(stream1, stream2, 1024, function(arg) {
	Ti.API.info("bytes processed: " + arg.bytesProcessed);
	Ti.API.info("Event: " + JSON.stringify(arg, false, 2));
});

Please clarify expected behavior.