fix two bugs in block image updater

The computation of file offsets was overflowing for partitions larger
than 2 GB.  The parsing of the transfer file could fail at the end if
the data happened to not be properly null-terminated.

Bug: 16984795
Change-Id: I3ce6eb3e54ab7b55aa9bbed252da5a7eacd3317a
1 file changed