When mPackageName is null, mFinish is true. OnResume() doesn't
invoke refreshUI(). It causes uninstall button is still enabled.
The solution is hiding AppButtonsPreference when mFinish is true.
Fixes: 138524326
Test: make RunSettingsRoboTests ROBOTEST_FILTER
Change-Id: I9759e53f002afbd4c88d8d536df3bf01c343135e
(cherry picked from commit 88228c3399)