Fix panic in k6/execution

[olegbespalov]

What?

Fix a minor panic that could happen if try to get insides about the exec.vu.iterationInScenario in setup method

In that case, we will return 0 as all other vu.* properties do.

Why?

Panics are bad.

Resolves: #2924

[codecov-commenter]

Codecov Report

Merging #2926 (70b510f) into master (eb2a54d) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 70b510f differs from pull request most recent head b5b155d. Consider uploading reports for the commit b5b155d to get more accurate results

@@           Coverage Diff           @@
##           master    #2926   +/-   ##
=======================================
  Coverage   76.87%   76.88%           
=======================================
  Files         225      225           
  Lines       16894    16895    +1     
=======================================
+ Hits        12987    12989    +2     
+ Misses       3076     3074    -2     
- Partials      831      832    +1     

Flag	Coverage Δ
ubuntu	76.81% <100.00%> (+<0.01%)	⬆️
windows	76.66% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
js/modules/k6/execution/execution.go	83.61% <100.00%> (+0.09%)	⬆️
api/v1/metric.go	54.54% <0.00%> (-9.10%)	⬇️
lib/executor/ramping_arrival_rate.go	96.52% <0.00%> (-0.87%)	⬇️
js/modules/k6/ws/ws.go	86.66% <0.00%> (+0.57%)	⬆️
lib/executor/vu_handle.go	95.32% <0.00%> (+0.93%)	⬆️
metrics/metric_type.go	82.45% <0.00%> (+3.50%)	⬆️

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[imiric]

LGTM 👍