fix deconflicting variable name for slot fallback (#4564)

Author: tanhauhau

src/compiler/compile/render_dom/wrappers/Slot.ts

@@ -38,6 +38,7 @@ export default class SlotWrapper extends Wrapper {
 				name: this.renderer.component.get_unique_name(`fallback_block`),
 				type: 'fallback'
 			});
+			renderer.blocks.push(this.fallback);
 		}
 
 		this.fragment = new FragmentWrapper(
@@ -115,7 +116,6 @@ export default class SlotWrapper extends Wrapper {
 
 		if (this.fallback) {
 			this.fragment.render(this.fallback, null, x`#nodes` as Identifier);
-			renderer.blocks.push(this.fallback);
 		}
 
 		const slot = block.get_unique_name(`${sanitize(slot_name)}_slot`);

test/runtime/samples/component-slot-fallback-3/Inner.svelte

@@ -0,0 +1,6 @@
+<slot>
+	<div>Hello</div>
+	<div>world</div>
+	<div>Bye</div>
+	<div>World</div>
+</slot>

test/runtime/samples/component-slot-fallback-3/_config.js

@@ -0,0 +1,6 @@
+export default {
+	html: `
+	<div>Hello World</div>
+	<div>Hello</div><div>world</div><div>Bye</div><div>World</div>
+	`,
+};

test/runtime/samples/component-slot-fallback-3/main.svelte

@@ -0,0 +1,9 @@
+<script>
+	import Inner from "./Inner.svelte";
+</script>
+
+<Inner>
+	<div>Hello World</div>
+</Inner>
+
+<Inner></Inner>