storage: One more persist error code path discovered
storage: One more persist error code path discovered

Also, in that code path, set chunkDescsOffset to 0 rather than -1 in
case of "dropped more chunks from persistence than from memory" so
that no other weird things happen before the series is quarantined for
good.

brancz/prometheus,yanghongkjxy/prometheus,Stackdriver/stackdriver-prometheus,GoogleCloudPlatform/prometheus,prometheus/prometheus,dsymonds/prometheus,AlekSi/prometheus,alileza/prometheus,Conorbro/prometheus,agaoglu/prometheus,keegancsmith/prometheus,JavierZunzunegui/prometheus,yanghongkjxy/prometheus,gottwald/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,prometheus/prometheus,kangwoo/prometheus,tomwilkie/prometheus,SaltedMan/prometheus-annotated,AlekSi/prometheus,dsymonds/prometheus,Stackdriver/stackdriver-prometheus,gottwald/prometheus,Gouthamve/prometheus,tomwilkie/prometheus,Gouthamve/prometheus,agaoglu/prometheus,kangwoo/prometheus,dsymonds/prometheus,kangwoo/prometheus,brancz/prometheus,Conorbro/prometheus,GoogleCloudPlatform/prometheus,gottwald/prometheus,alileza/prometheus,amorken/prometheus,gottwald/prometheus,keegancsmith/prometheus,alileza/prometheus,agaoglu/prometheus,amorken/prometheus,prometheus/prometheus,Gouthamve/prometheus,SaltedMan/prometheus-annotated,Gouthamve/prometheus,yanghongkjxy/prometheus,Colstuwjx/prometheus,Stackdriver/stackdriver-prometheus,JavierZunzunegui/prometheus,tomwilkie/prometheus,Colstuwjx/prometheus,GoogleCloudPlatform/prometheus,SaltedMan/prometheus-annotated,GoogleCloudPlatform/prometheus,keegancsmith/prometheus,amorken/prometheus,AlekSi/prometheus,keegancsmith/prometheus,dsymonds/prometheus,Colstuwjx/prometheus,agaoglu/prometheus,Stackdriver/stackdriver-prometheus,kzittritsch/prometheus,JavierZunzunegui/prometheus,brancz/prometheus,alileza/prometheus,prometheus/prometheus,yanghongkjxy/prometheus,amorken/prometheus,kangwoo/prometheus,tomwilkie/prometheus,Conorbro/prometheus,AlekSi/prometheus,kzittritsch/prometheus,Conorbro/prometheus,keegancsmith/prometheus,brancz/prometheus,kzittritsch/prometheus,Colstuwjx/prometheus,alileza/prometheus,JavierZunzunegui/prometheus,SaltedMan/prometheus-annotated,kzittritsch/prometheus