Handles onFailure case of getting wallpaper color

- Use a fixed bitmap size to be stored, so that the full preview won't decode the asset, uses tha catched result.
- If returns null wallpaper color, uses light color as default.

Test: Manually
Fixes: 157889638
Change-Id: Iaf513d79eb2d6154b0bf50e333f607205c3eea9d