Use deep shortcuts' icons as a fallback when updating

We already do this when loading, but now we also do it when
getting callbacks that potentially change the shortcut icon.
These callbacks first check the pinned shortcut info, but if
there is no icon there we now fall back to the current icon
instead of the default icon.

Bug: 62814533
Change-Id: I777adedf4b7f93dbaddb98a993eda34d59dcc173