Crash when loading an image caption with a list inside (ListProperties)

[oleq]

📝 Provide detailed reproduction steps (if any)

1. Go to https://ckeditor5.github.io/docs/nightly/ckeditor5/latest/features/lists/lists.html#demo-2
2. Set the following data

<figure class="image"><img src="https://33333.cdn.cke-cs.com/rc1DFuFpHqcR3Mah6y0e/images/93c337f3c2eb83f436edba7e778a5983d212dd8ab79859d7.png"  width="1208"><figcaption><ul><li>foo</li></ul></figcaption></figure>

✔️ Expected result

Silence.

❌ Actual result

spector.js:2 Uncaught TypeError: Cannot read properties of null (reading 'start')
    at e.on.priority (snippet.js:4:605515)
    at Ec.fire (snippet.js:4:5541)
    at Ec._convertItem (snippet.js:4:231683)
    at Ec._convertChildren (snippet.js:4:232140)
    at Object.convertChildren (snippet.js:4:230260)
    at Pc.upcastDispatcher.on.priority (snippet.js:4:236015)
    at Ec.fire (snippet.js:4:5541)
    at Ec._convertItem (snippet.js:4:231683)
    at Ec._convertChildren (snippet.js:4:232140)
    at Object.convertChildren (snippet.js:4:230260)

❓ Possible solution

List properties upcast converter tries to upcast attributes despite the "parent" list element not being upcasted in the first place (e.g. disallowed in the image caption). We need to check whether the model range exists first in the converter.

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