COMPRESS-644 -- do not allow zero by entries when detecting magic-less tar

[tballison]

When relying on reading the first record from a tar file and then verifying the checksum as proof that the file is a tar file, require that the record have more than zero bytes.

[codecov-commenter]

Codecov Report

Merging #386 (2204031) into master (1223b72) will decrease coverage by 0.01%. The diff coverage is 42.85%.

@@             Coverage Diff              @@
##             master     #386      +/-   ##
============================================
- Coverage     80.45%   80.44%   -0.01%     
- Complexity     6723     6724       +1     
============================================
  Files           343      343              
  Lines         25312    25316       +4     
  Branches       4107     4109       +2     
============================================
+ Hits          20365    20366       +1     
+ Misses         3366     3365       -1     
- Partials       1581     1585       +4     

Impacted Files	Coverage Δ
...s/compress/compressors/CompressorOutputStream.java	100.00% <ø> (ø)
...mmons/compress/archivers/ArchiveStreamFactory.java	89.30% <33.33%> (-2.26%)	:arrow_down:
...mpressors/pack200/InMemoryCachingStreamBridge.java	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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