Handle error when More Galleries data can't be fetched

When most viewed galleries request made from the client, is failed, we are returning null. But before the fetch call is made we have already placed a `Placeholder` section with a height quite near the resulting component. So returning null is going to remove the `Placeholder` hence causing layout shift.

We need to handle the error differently to ovoid this layout shift.

More details in @JamieB-gu 's comment in [here](https://github.com/guardian/dotcom-rendering/pull/14545#discussion_r2406830588)