fix: optional postMessage transfer arg

[codebytere]

Description of Change

Closes #32427.

Fixes an issue where attempts to use ipcRenderer.postMessage without the ostensibly optional transfer argument would throw TypeError: Invalid value for transfer. This was happening because absl::optional value checks consider undefined a value, so we were incorrectly trying to convert undefined into an array of transferrable objects. This is fixed by checking explicitly for transfer being undefined.

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are changed or added
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Fixed an issue where ipcRenderer.postMessage would throw errors when the transfer argument was not passed.

[codebytere]

Failure not relevant:

tag loads devtools extensions registered on the parent window

is a known flake.

[release-clerk]

Release Notes Persisted

Fixed an issue where ipcRenderer.postMessage would throw errors when the transfer argument was not passed.

[trop]

I have automatically backported this PR to "14-x-y", please check out #32457

[trop]

I have automatically backported this PR to "15-x-y", please check out #32458

[trop]

I have automatically backported this PR to "17-x-y", please check out #32459

[trop]

I have automatically backported this PR to "16-x-y", please check out #32460