fix error when getting product thumbnails by url key

[vacla]

Description

Made it so that it won't error anymore on a null value in an array when sending it, as Magento backend will just ignore this and send an empty item for this back.

Related Issue

Closes #4307 .

Acceptance

Verification Stakeholders

Specification

Verification Steps

Test scenario(s) for direct fix/feature

1. Login in account
2. Place order with 1 product
3. Delete this product out of magento
4. Go to order history page
5. See no error anymore in console

Checklist

• I have added tests to cover my changes, if necessary.
• I have added translations for new strings, if necessary.
• I have updated the documentation accordingly, if necessary.

[pwa-studio-bot]

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[glo82145]

This issue has been fixed and merged, hence closing this PR