freezer: handle exception in locks file format

Safeguard /proc/locks processing from wrongly formatted /proc/locks
files

Bug: 179171387
Test: could not reproduce the issue, but verified that no crashes
occurred in a prolonged test (4hrs+)

Change-Id: Ia8a12903f2e520e51780c8b05876aa1c9083e92b
(cherry picked from commit fb4f4073)