Fix possible java.lang.ArithmeticException when parsing ZGC Log

[lpaladin]

Reproducible when feeding with a log like

[1.592s][info][gc] Using The Z Garbage Collector
[3.321s][info][gc] GC(0) Garbage Collection (Metadata GC Threshold) 332M(2%)->30M(0%)
[5.492s][info][gc] GC(1) Garbage Collection (Metadata GC Threshold) 1044M(6%)->68M(0%)

[codecov-io]

Codecov Report

Merging #238 into master will not change coverage.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master     #238   +/-   ##
=========================================
  Coverage     70.43%   70.43%           
  Complexity     1518     1518           
=========================================
  Files           145      145           
  Lines          8596     8596           
  Branches       1389     1389           
=========================================
  Hits           6055     6055           
  Misses         1961     1961           
  Partials        580      580

Impacted Files	Coverage Δ	Complexity Δ
...perf/gcviewer/imp/DataReaderUnifiedJvmLogging.java	81.05% <100%> (ø)	66 <0> (ø)	⬇️

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