[PATCH 3/5] pstore: handle zero-sized prz in series

Corrects a problem wih ramoops_pstore_read failing to
return the next in a prz series after first zero-sized
entry, not venturing to the next non-zero entry.

Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Change-Id: Iedce3b94c13917da33be44e1d80811757774c793