Themes: Map themed icon to app after upgrade

Before this patch, applying an icon theme and then upgrading an app would
cause the app to lose its themed icon.

Change-Id: Ia76a33d0fb731720aa735e9dd9596bc5d2e75d9f
(cherry picked from commit 88a5574d18dd1fa48880ffa4e32b4f48a369eaf8)