Can't render 2 notebooks?

[sbatten]

refs #91328

Open 2 notebooks side by side:

e.g. runCode_iframe_form_15.ipynb and runCode-slim.ipynb

iframes fail to render

[mjbvz]

@rebornix Can you please test the change I just pushed. The error does not happen reliably so I'm not sure if I fixed it or not

[rebornix]

It seems it's fixed. I'll close it for now, thanks for the quick fix!

[rebornix]

Verification:

• Open a notebook which contains html outputs
• Split the editor
• Make sure the html outputs are rendered in both panels.