archive_read: Handle sparse holes at end of file

archive_read: Handle sparse holes at end of file

If a sparse hole is located at the end of an entry, then the tar
parser returns ARCHIVE_EOF while updating the offset where 0 bytes of
data will follow.

If archive_read_data encounters such an ARCHIVE_EOF return value, it
has to recheck if the offsets (data offset and output offset) still
match. If they do not match, it has to keep filling 0 bytes.

This changes assumes that it's okay to call archive_read_data_block
again after an EOF. As far as I understood the parsers so far, this
should be okay, since it's always ARCHIVE_EOF afterwards.

Fixes https://github.com/libarchive/libarchive/issues/1194

Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>