Commit 10e3226ba1 added padding to incremental backups to ensure the
block data is properly aligned. The code in sendFile() however failed to
consider that the header may be a multiple of BLCKSZ and thus already
aligned, adding a full BLCKSZ of unnecessary padding.
Not only does this make the incremental file a bit larger, but the other
places calculating the amount of padding did realize it's not needed and
did not include it in the formula. This resulted in pg_basebackup
getting confused while parsing the data stream, trying to access files
with invalid filenames (e.g. with binary data etc.) and failing.
cd4b6af620