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Describe the bug
The onLoad listener for <img /> isn't removed after <img /> unmount.

timeline:

img mount -> start loading image -> img unmount -> finish loading image -> onLoad fires

To Reproduce
https://codesandbox.io/s/kind-jepsen-kqwte?file=/src/index.js

Steps to reproduce the behavior:

1. Keep refresh the page, and at some time the imgRef === null, which means when onLoad fires, <img /> is already unmounted

Expected behavior
all listeners (including onLoad) should be removed or not fired after unmount