Fix crashes related to ExternalSourcesDetails.

- ExternalSourcesSettingsTest crashes due to the package moved of
ExternalSourcesDetails. Corresponding xml has been updated in previous
CLs. So, reverting the suppress tag for the test class.
- ExternalSourcesDetails can be launched directly with
MANAGE_UNKNOWN_APP_SOURCES intent, and client can pass in invalid
package while launching ExternalSourcesDetails. Need to check whether
the app info is invalid before we try to launch the fragment.
- also fix test failure for not founding the app list as list object
type and id had been changed.

Change-Id: Id7787ca889f770e10d7a8e9fbf8dc79c9d6e884d
Fixes: 70383636
Test: make RunSettingsRoboTests, make SettingsUnitTests