Handle null parentElement for selection anchor

[hubgit]

In the selectionchange handler that's added to the document by TextLayerBuilder, there is a line which accesses anchor.parentElement.closest(".textLayer").

This throws an error if anchor.parentElement is null, which can happen if the selection is inside a shadow root - I can reproduce it by selecting text inside Grammarly's popover on a page where PDF.is is being used.

The error is only seen in non-Firefox browsers, as there is a line which returns earlier in Firefox.

This change handles the null parentElement gracefully, to avoid throwing the error.

[timvandermeij]

/botio-linux preview

[moz-tools-bot]

From: Bot.io (Linux m4)

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Received

Command cmd_preview from @timvandermeij received. Current queue size: 0

Live output at: http://54.241.84.105:8877/a1ada5b8ae11d90/output.txt

[moz-tools-bot]

From: Bot.io (Linux m4)

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Success

Full output at http://54.241.84.105:8877/a1ada5b8ae11d90/output.txt

Total script time: 1.01 mins

Published

• Viewer: http://54.241.84.105:8877/a1ada5b8ae11d90/web/viewer.html
• Viewer (legacy): http://54.241.84.105:8877/a1ada5b8ae11d90/legacy/web/viewer.html

[timvandermeij]

/botio integrationtest

[moz-tools-bot]

From: Bot.io (Linux m4)

---

Received

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

Live output at: http://54.241.84.105:8877/297883ec4e536b7/output.txt

[moz-tools-bot]

From: Bot.io (Windows)

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Received

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

Live output at: http://54.193.163.58:8877/22a3fb8e708c06e/output.txt

[moz-tools-bot]

From: Bot.io (Linux m4)

---

Success

Full output at http://54.241.84.105:8877/297883ec4e536b7/output.txt

Total script time: 9.21 mins

• Integration Tests: Passed

[moz-tools-bot]

From: Bot.io (Windows)

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Success

Full output at http://54.193.163.58:8877/22a3fb8e708c06e/output.txt

Total script time: 20.43 mins

• Integration Tests: Passed

[timvandermeij]

Thank you for your contribution!