Prevent app pairs rank from resetting on Launcher model reload

This fixes a bug where app pairs rank was mistakenly reset upon Launcher reload, causing app pairs to launch with the wrong ratio.

Bug: 274835596
Test: App pairs restore properly even after Launcher restart
Flag: ENABLE_APP_PAIRS
Change-Id: I5d37190cd994628886f77e089c71fc5e5dddc03e