Fix a bootloop problem when /data/system/usagestats/usage-history.xml is empty.
This often occurs after an incomplete reboot/shutdown or battery pull.

Change-Id: I4f01151f4051df4ae1b85fa460ec7a9e70122878

Ported from cm-10.2

Patchset: 1
http://review.cyanogenmod.org/#/c/55114/