Fixed benchmark bugs

[aria42]

Fixes following issues

• On decoding error, report-tsv-line would always NPE since result doesn't have keys other than :error, resolved by adding codec/version to map in error case
• Wrong number of args to generate-sample-data
• Ensure data tsv exists earlier to avoid IO failure on slurp-ing non-existent file
• Fallback correctly to max-size which was causing the argument default to "0" which generated trivial data
• Default to #{} when no existing benchmarked blocks exist

Now you can generate data and bench from scratch without uncaught exception

[codecov-io]

Codecov Report

Merging #10 into develop will not change coverage. The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop      #10   +/-   ##
========================================
  Coverage    99.86%   99.86%           
========================================
  Files           13       13           
  Lines          748      748           
  Branches         1        1           
========================================
  Hits           747      747           
  Partials         1        1

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