Fixes ENYO-526

## Issue
The `value` from the ExpandableIntegerPicker is blindly routed to the contained IntegerPicker via a binding but IntegerPicker isn't designed to handle non-integer values.

## Fix
Since the value-less state is unique to the expandable picker API, only pass the `value` to the picker when the value is valid. Also update `openChanged` to set the value on open if it's currently value-less.

Enyo-DCO-1.1-Signed-off-by: Ryan Duffy (ryan.duffy@lge.com)
But IntegerPicker has already set the initial value as -1 in 
https://github.com/enyojs/moonstone/blob/ENYO-526-ryanjduffy/source/ExpandableIntegerPicker.js#L80