Fix Custom HTML error when block is empty

[Rahmon]

Description

Fix Custom HTML block error when block is empty and Preview button is clicked.

Closes: #7277

How has this been tested?

This has been tested with "npm test" and manually on Chrome and Firefox

Types of changes

Bug fix

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.

[noisysocks]

Thanks @Rahmon!

[aduth]

So was the error caused by property access on the undefined value?

If so, shouldn't we also need to consider the .tagName property access in the condition immediately preceding this one?

[Rahmon]

potentialIframe && potentialIframe.tagname && 'IFRAME' === potentialIframe.tagName

is that way, right?

[noisysocks]

If so, shouldn't we also need to consider the .tagName property access in the condition immediately preceding this one?

potentialIframe isn't undefined until it's re-assigned in the condition above.

[aduth]

What is this code even doing? aspectRatio is unused. width is assigned to 100% but should already be effected this way via the appended styles a few lines below anyways.

Can we just remove it?

[noisysocks]

cc. @notnownikki

[notnownikki]

@aduth aspectRatio is used in sendResize to preserve the aspect ratio of iframes with an initial set width and height, so they can be resized to 100% width and keep the correct height. This is important when embedding content such as YouTube videos.

[notnownikki]

Admittedly, the code to discover the first iframe is janky. Sorry about that.