Fix document elements check to prevent WYSIWYG error on IE

[krzksz]

Description (*)

When creating a document using DomParser's parseFromString method from an empty string, IE 11 returns a document which both head and body elements are null, which caused the errors.

Fixes #13209

Fixed Issues (if relevant)

1. Wysiwyg editor fails on IE11 #13209: Wysiwyg editor fails on IE11

Manual testing scenarios (*)

1. Open Magento admin panel on Internet Explorer 11.
2. Go to any WYSIWYG editor field, e.g. CMS page content editor.
3. Start typing.
4. No error popup is displayed.

Questions or comments

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds are green)

[m2-assistant]

Hi @krzksz. Thank you for your contribution
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[krzksz]

@magento give me test instance

[magento-engcom-team]

Hi @krzksz. Thank you for your request. I'm working on Magento instance for you

[magento-engcom-team]

Hi @krzksz, here is your new Magento instance.
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[magento-engcom-team]

Hi @lbajsarowicz, thank you for the review.
ENGCOM-6310 has been created to process this Pull Request
✳️ @lbajsarowicz, could you please add one of the following labels to the Pull Request?

Label	Description
Auto-Tests: Covered	All changes in Pull Request is covered by auto-tests
Auto-Tests: Not Covered	Changes in Pull Request requires coverage by auto-tests
Auto-Tests: Not Required	Changes in Pull Request does not require coverage by auto-tests

[engcom-Bravo]

Hello @lbajsarowicz. Would You please add an appropriate label to this PR. Thank You.

[lbajsarowicz]

Hello @lbajsarowicz. Would You please add an appropriate label to this PR. Thank You.

Label added.

[engcom-Bravo]

Hello @krzksz. Thank You for Your contribution. Please cover Your PR with the appropriate Auto-Tests in order for us to be able to process it further. Thank You.

[krzksz]

Alright, I'm up for the challenge! 😄

[krzksz]

So I tried to prepare tests for this scenario but there are 2 issues with covering it:

1. MFTF documentation states that A Selenium web driver cannot enter data to fields with WYSIWYG. so I am not able to test it.
2. Even if I where then I believe tests are not executed on IE, where error occurs.

[krzksz]

@engcom-Bravo I believe this can be picked up for QA and merge now.

[engcom-Bravo]

✔️ QA Passed

[m2-assistant]

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