Fix creation of debugging comment for elements without children

src/compile/render-dom/wrappers/shared/create_debugging_comment.ts

@@ -16,7 +16,7 @@ export default function create_debugging_comment(
 	let d;
 
 	if (node.type === 'InlineComponent' || node.type === 'Element') {
-		d = node.children[0].start;
+		d = node.children.length ? node.children[0].start : node.start;
 		while (source[d - 1] !== '>') d -= 1;
 	} else {
 		d = node.expression ? node.expression.node.end : c;

test/runtime/samples/component-slot-empty-b/Nested.svelte

@@ -0,0 +1,3 @@
+<div>
+	<slot name="slot1" />
+</div>

test/runtime/samples/component-slot-empty-b/_config.js

@@ -0,0 +1,3 @@
+export default {
+	html: `<div><input slot="slot1"></div>`
+};

test/runtime/samples/component-slot-empty-b/main.svelte

@@ -0,0 +1,6 @@
+<script>
+	import Nested from "./Nested.svelte";
+</script>
+<Nested>
+	<input slot="slot1">
+</Nested>