Slightly improve the performance of removeNullCharacters

[calixteman]

Most of the strings shouldn't contain special chars (<= 0x1F) so we can have a fast path which just checks if the string contains at least one such a char.

[calixteman]

I profiled pdf.pdf with a sampling interval equals to 0.1ms.
Here's a profile without the patch:
https://share.firefox.dev/3Quo0Mb
and one with the patch:
https://share.firefox.dev/3tMyfCI
The function is now around ~3 times faster.

[Snuffleupagus]

It might not matter all that much, performance wise, but given how and where this helper function is being used do we still need the following part of it?

pdf.js/web/ui_utils.js

Lines 216 to 219 in f098121

	if (typeof str !== "string") {
	console.error(`The argument must be a string.`);
	return str;
	}

(This function was originally placed in src/shared/util.js, hence the additional validation.)

[Snuffleupagus]

r=me, thank you!

[calixteman]

/botio integrationtest

[moz-tools-bot]

From: Bot.io (Windows)

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Received

Command cmd_integrationtest from @calixteman received. Current queue size: 0

Live output at: http://54.193.163.58:8877/8578b21c45edd38/output.txt

[moz-tools-bot]

From: Bot.io (Linux m4)

---

Received

Command cmd_integrationtest from @calixteman received. Current queue size: 1

Live output at: http://54.241.84.105:8877/8cc62fdc5c36313/output.txt

[moz-tools-bot]

From: Bot.io (Linux m4)

---

Success

Full output at http://54.241.84.105:8877/8cc62fdc5c36313/output.txt

Total script time: 5.56 mins

• Integration Tests: Passed

[moz-tools-bot]

From: Bot.io (Windows)

---

Failed

Full output at http://54.193.163.58:8877/8578b21c45edd38/output.txt

Total script time: 18.78 mins

• Integration Tests: FAILED