Always filter out all zero blocks from old_file_extents.

Even though we are allowed to read the old blocks multiple times for
non-inplace update, we should still skip those blocks that are all
zero.

Bug: 120465293
Test: no zero blocks in src_extents in delta payload
Change-Id: I48bdc06680316d2c9b373e9d929fdff1ad797a55
(cherry picked from commit ba0fc92e)
(cherry picked from commit ce59e761da8e8dd0fe07f5cb21915768ce430cce)