Constant flicker on broken image

Nobody has claimed this yet.

**Describe the bug**
If any of the images higher up in the column are broken, the rest of the column starts flickering

**To Reproduce**
Sandbox here: https://codesandbox.io/p/sandbox/sparkling-cache-3cpp8v

(I'm not sure why some of the images are broken, but that seems to be a separate issue.)

**Expected behavior**
No flicker.

**Screenshots**


(Note that when live the column continues to flicker; it's only the GIF which has come to an end.)

**Desktop:**

- OS: Windows
- Browser Firefox/Chrome
- Version Firefox 130.0.1 / Chrome 129.0.6668.59 / Masonic 4.0.1

**Smartphone:**

(not tested)

**Additional context**

This doesn't happen with the basic `Masonry` component, only with `MasonryScroll`.

AFAICT the initial measurement doesn't take into account the height of the broken image placeholder inserted by the browser. When the browser gets around to inserting the placeholder, that triggers a React re-render; in which the measurement again doesn't include the height of the placeholder.

Setting `alt` to an empty or short string stops the flickering, presumably because the browser doesn't render the placeholder ([other methods for doing the same thing might also work](https://stackoverflow.com/q/22051573/111794)):


If there are no broken images in the initial viewport, scrolling down until a broken image comes into view triggers the flicker.

Moving to a different browser tab or a different window and then back, stops the flicker.

Start with the provided CodeSandbox reproduction and inspect the MasonryScroller implementation, especially its initial measurement and re-render behavior when an image is broken. Compare it with the basic Masonry component and verify the fix by loading broken images both in the initial viewport and while scrolling; done means the column no longer flickers.

Written by the indexing model from the issue text.