handle cargo check case where no code is present

[thefarwind]

cargo-check.log
When using the cargo tool in the warnings next generation plugin configured as follows:

steps {
  sh 'cargo check --message-format json > cargo-check.log'
}
post {
  always {
    recordIssues tool: cargo(pattern: 'cargo-check.log')
  }
}

I was receiving the following error message:

JSONObject["code"] is not a JSONObject.

I tracked this crash to "warning: 1 warning emitted" line from the cargo check output, which instead of having an error code, has a null error code.

This change modified the cargo check parser to ignore compiler-messages which have a null code field. It also added an appropriate test message to verify compiler-messages with a null code are ignored, as well as two additional test messages of additional message types which appeared in the cargo-check output.

[codecov]

Codecov Report

Merging #502 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master     #502   +/-   ##
=========================================
  Coverage     90.27%   90.27%           
- Complexity     1517     1518    +1     
=========================================
  Files           171      171           
  Lines          4513     4515    +2     
  Branches        491      492    +1     
=========================================
+ Hits           4074     4076    +2     
  Misses          284      284           
  Partials        155      155           

Impacted Files	Coverage Δ	Complexity Δ
...du/hm/hafner/analysis/parser/CargoCheckParser.java	100.00% <100.00%> (ø)	10.00 <0.00> (+1.00)

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[uhafner]

Thanks for fixing!