Memory Usage by apps no longer shows empty icon

ProcessStatsPreference will now fallback to a
default icon instead of an empty icon. Logging
was added to be able to identify what causes
list to add entries with no text.

Test: Manual, requires installing -> uninstalling an app
Bug: 31812426
Change-Id: Ia1b147ba7a552ec4880776ebf8dba6745154117a