HPCC-8957 - Compressed files being published with incorrect crc

When block compression files are created, implicitly a crc of
0 is always the result. The published crc should be ~<crc-val>
but in case of compressed files it was publishing 0.

This was noticed only by VerifyFile

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>