Void element 'children' get hydrated

[Rich-Harris]

Describe the bug
Svelte generates code that hydrates the children of <img> elements and other void elements, even though there can't be any by definition.

To Reproduce
https://svelte.dev/repl/f5c696a56a234934a9556be6a696e5db?version=3.12.1

Expected behavior

	return {
		c() {
			img = element("img");
			this.h()
		},

		l(nodes) {
			img = claim_element(nodes, "IMG", { src: true }, false);
-			var img_nodes = children(img);
-
-			img_nodes.forEach(detach);
			this.h();
		},

		h() {
			attr(img, "src", "donuts.jpg");
		},

Severity
Mostly harmless, but easily fixed