logcat: continue where we left off

Issue introduced as part of new logcatd functionality in
commit f3555d9427425c2cba9600ceffb49305c440aa4a

Faulty logic, add a gTest to confirm.

Bug: 19608716
Change-Id: Ic1b97def25e03e69faae4398a3dff2ff0f88545e
2 files changed