Fix color options showing default colors (2/3)

Fix color options showing default colors for certain wallpapers.
Computing color info using thumbnail should only be used to get initial
colors while actual colors are being loaded. Actual colors should be
obtained from wallpaper manager.

Bug: 282999514
Test: manually verified, see bug
Change-Id: Ib54e354202108a8d6eb66bdfe485e65ceaef0a55