Editor: Fix drag and drop to the top of the page

[karthikeya-io]

What?

Closes #71198

Why?

• The drag and drop feature in Editor doesn't work as expected if useBlockProps used incorrectly or if the block doesn't render any markup.
• Logs the following error in console Uncaught TypeError: Cannot read properties of null (reading 'getBoundingClientRect').

How?

• Guard getElementById calls and return null if no block element exists and add null-safe checks around dropZoneElement.getBoundingClientRect()
• In PostCommentsLinkEdit:
  • Remove early return null and render warning.

Testing Instructions

1. While editing the template add the Comments Link block
2. Check if drag and drop works as expected
3. Confirm no errors in console

Testing Instructions for Keyboard

Screenshots or screencast

Before and After

Screen.Recording.2025-08-19.at.1.51.27.AM.mov

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[talldan]

Works great, thanks for the fix, and for finding the block with the issue.

I also tested the drag and drop changes without the block fix, and it works well, so it means drag and drop will work better if a third party block might have this kind of bug.