Prevent panic when 'options' value is nil

[joanlopez]

What?

It early returns when options is nil, to prevent reaching the point where json.Marshal(v.Export()) with v == nil.

Why?

To prevent it from panicking.

In v0.52, that code was slightly different: https://github.com/grafana/k6/blob/v0.52.0/js/bundle.go#L176, and so the value received was goja.valueUndefined, which is enough for not panicking when calling json.Marshal(v.Export()).

Since changes introduced in v0.53, v is nil, and thus it panics.

Additional comments

Another approach that I suggested was changing the behavior of SourceTextModuleInstance.GetBindingValue in Sobek, so it returns sobek.Undefined() when no getter is found, but @mstoykov had doubts around the general correctness of that approach, so I guess the least intrusive way to prevent such panics here is this.

Checklist

• I have performed a self-review of my code.
• I have added tests for my changes.
• I have run linter locally (make lint) and all checks pass.
• I have run tests locally (make tests) and all tests pass.
• I have commented on my code, particularly in hard-to-understand areas.

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