Handle an edge case that can reset settings provider data

If the AtomicFile does the rename and fails when writing the
original, make sure we can at least use the backup on reboot.

Bug: 63753300
Test: Stop shell, move settings_global.xml to backup, start shell.
Change-Id: I2049b48af05161bb2c68717a71c1700a95150a6c
3 files changed