Fix dumpio: true logs about #createBundleFallback

[timvandermeij]

In PR #18260 we enabled dumpio: true for Puppeteer. This option forwards the browser logs to Node's log stream so that we can see any warnings/errors that are logged in e.g. the web console. This surfaced a few interesting issues that we should fix before we enable that further due to the spammy nature of said logs.

This issue tracks the following often repeated log from http://54.241.84.105:8877/34fcd127eefeaf9/output.txt:

JavaScript error: http://127.0.0.1:41223/build/generic/web/viewer.mjs, line 3023: Error: Not implemented: #createBundleFallback

I have tracked the problem down to

pdf.js/web/genericl10n.js

Line 79 in 06800cd

yield this.#createBundleFallback(lang);

being triggered, which in turn triggers

pdf.js/web/genericl10n.js

Lines 110 to 112 in 06800cd

	if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("TESTING")) {
	throw new Error("Not implemented: #createBundleFallback");
	}

and because we're in testing mode the exception is thrown.

Both code paths were introduced in 97c2ce9 but unfortunately I don't know enough about the L10n bundle handling to be able to tell for sure what the issue is. However, in debugging this I found that we in fact have a valid bundle for en-us just before at

pdf.js/web/genericl10n.js

Line 76 in 06800cd

yield bundle;

which made me wonder why we also try to create a fallback bundle for this language, and thought: are we perhaps missing a continue after the yield here? If I look at the situation before the patch, see 97c2ce9#diff-28e788fc43e67c197d60ffb3054ffb599f083341963c64d156e7a87a0ced98ceR78, we would always continue implicitly after the yield, but now it basically falls through to the fallback bundle creation.

This might very well be intended though, and this is the part I don't know. I'm also not sure why there is a dedicated testing path in this code, because if we fall through we'll always get here in testing mode too. @Snuffleupagus Do you perhaps have ideas for this, since you probably know this code a lot better than I do?