Respect workerSrc if set

[tonyjin]

Respect user-defined workerSrc over internal overrides.

Resolves #9443.

[timvandermeij]

This change looks reasonable to me, but since I'm not too familiar with the worker logic, I would like a second pair of eyes here just to be sure I'm not missing anything.

[Snuffleupagus]

/botio test

[pdfjsbot]

From: Bot.io (Linux m4)

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Received

Command cmd_test from @Snuffleupagus received. Current queue size: 0

Live output at: http://54.67.70.0:8877/e370d2df7eeb250/output.txt

[pdfjsbot]

From: Bot.io (Windows)

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Received

Command cmd_test from @Snuffleupagus received. Current queue size: 0

Live output at: http://54.215.176.217:8877/98042e3c69b353b/output.txt

[pdfjsbot]

From: Bot.io (Windows)

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Success

Full output at http://54.215.176.217:8877/98042e3c69b353b/output.txt

Total script time: 23.97 mins

• Font tests: Passed
• Unit tests: Passed
• Regression tests: Passed

[pdfjsbot]

From: Bot.io (Linux m4)

---

Success

Full output at http://54.67.70.0:8877/e370d2df7eeb250/output.txt

Total script time: 38.90 mins

• Font tests: Passed
• Unit tests: Passed
• Regression tests: Passed

[Snuffleupagus]

The current situation, where the workerSrc option is being silently ignored in some cases seems far from ideal to me.

I suppose that the only caveat here would be if there's API consumers that managed to set an invalid workerSrc, and where the current logic thus "saved" them.
However I'm not too worried about that, and besides my impression from questions/issues over the years is that it's a lot more common for users to have trouble because they did not set the workerSrc option at all.

The above is thus a somewhat long-winded way of saying that I think this change is fine. Thanks for the patch!

[tonyjin]

Thanks! I appreciate the context.