Avoid core/image PHP warnings

[aatanasovdev]

Description

Fixing PHP warnings when empty core/image blocks are used inside the WordPress Block editor.

Fixes: #89

Steps to Test

1. Add an empty core/image to a post (as shown in the below screenshot).
2. Go to the GraphQL IDE and execute the below example query. Please set a relevant id based on your instance.
3. Check the debug logs of your instance, and warnings shouldn't appear.
4. Set an attachment to the empty image block and ensure attributes like originalHeight are available when using the same query (check the attachment attributes screenshot).

Screenshots

core/image

attachment attributes

Example GraphQL Query

query GetPostContentBlocks {
  post(id: 6, idType: DATABASE_ID) {
    contentBlocks {
      blocks {
        tagName
        name
        attributes {
          name
          value
        }
      }
    }
  }
}

[chriszarate]

Tested and approved. Thanks for this fix! 👍