Fix the latest-posts block when imageDimensions is empty

[roo2]

Description

We found a bug when testing the Latest Posts block on WordPress.com that caused the block to fail to load: Automattic/wp-calypso#40127

There was a javascript crash caused by imageDimensions array having missing values for certain sizes that we try to access without a null check via imageDimensions[featuredImageSizeSlug].height

This PR adds a null check and defaults the image size to 0 if not values are found in the imageDimensions array.

How has this been tested?

I tested this by modifying imageDimensions to be empty. The Latest Posts block was then able to load, save, preview, etc.

After applying this fix, I did notice that if you select the named percentage sizes: "25%, 50%, 75%, 100%" then the image's max-width is set to 0px. I'm not sure if that is related but it could be fixed in addition to this null check.

I also noticed that the Width and Height values that the user enters set max-width and max-height css properties. This means that only the lowest value of Width and Height is used, If this is deliberate, I think it should be communicated better to the user :)

[noahtallen]

Great change! I think the test failures are affecting all Gutenberg PRs at the moment.

At any rate, it's important for folks to remember that since image dimensions are filterable on the server, it's possible for any of them to be filtered out.

I don't think any of the bugs you noted in the PR are related to these changes since the block has been working in the "normal" case. This doesn't change any of that behavior.

[noahtallen]

@roo2 could you rebase to try to fix tests? (I can merge once everything passes)

[roo2]

hey thanks for reminding me, yep the tests are passing now! :)

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Kudos!