Certain markup breaks the Source Editing mode

[maxbarnas]

📝 Provide detailed reproduction steps (if any)

1. Go to https://ckeditor.com/docs/ckeditor5/latest/features/general-html-support.html#demo,
2. In the Source Editing mode paste in the <dir><img contenteditable> into the editor,
3. Switch back to a regular mode.

✔️ Expected result

Editor parses markup and shows the results.

❌ Actual result

An error is thrown in the console and the Source Editing mode is not allowing to change editor's content.

Uncaught TypeError: Cannot read properties of null (reading 'getAttribute')
    at setAttributeOnItem (writer.js:1489)
    at Writer.setAttribute (writer.js:380)
    at preserveElementAttributes (image.js:102)
    at UpcastDispatcher.dispatcher.on.priority (image.js:90)
    at UpcastDispatcher.fire (emittermixin.js:199)
    at UpcastDispatcher._convertItem (upcastdispatcher.js:249)
    at UpcastDispatcher._convertChildren (upcastdispatcher.js:282)
    at UpcastDispatcher.<anonymous> (upcasthelpers.js:783)
    at UpcastDispatcher.fire (emittermixin.js:199)
    at UpcastDispatcher._convertItem (upcastdispatcher.js:249)

❓ Possible solution

Initial check points to the image integration plugin in ckeditor5-html-support.

[psmyrek]

The contenteditable is not needed. Any attribute in the img is enough to break the editor, i.e. <dir><img a>. Also <menu><img a> breaks the editor.