Set 'current' is the block have outros without intro (Fix #5120)

src/compiler/compile/render_dom/Block.ts

@@ -226,7 +226,9 @@ export default class Block {
 		const { dev } = this.renderer.options;
 
 		if (this.has_outros) {
-			this.add_variable({ type: 'Identifier', name: '#current' });
+
+			this.add_variable({ type: 'Identifier', name: '#current' },
+				this.chunks.intro.length === 0 ? x`true` : undefined);
 
 			if (this.chunks.intro.length > 0) {
 				this.chunks.intro.push(b`#current = true;`);

test/runtime/samples/reactive-mixed-slots/Component.svelte

@@ -0,0 +1,4 @@
+<slot name="named"/>
+<slot/>
+
+<script></script>

test/runtime/samples/reactive-mixed-slots/Empty.svelte

@@ -0,0 +1 @@
+<script></script>

test/runtime/samples/reactive-mixed-slots/_config.js

@@ -0,0 +1,15 @@
+export default {
+	html: `
+    <div slot='named'></div>
+    <a href='___init'>___init</a>
+    `,
+
+	test({ assert, component, target }) {
+        component.value = 'update';
+        
+        assert.htmlEqual(target.innerHTML, `
+            <div slot='named'></div>
+            <a href='___update'>___update</a>
+		`);
+	}
+};

test/runtime/samples/reactive-mixed-slots/main.svelte

@@ -0,0 +1,11 @@
+<script>
+    import Component from './Component.svelte';
+    import Empty from './Empty.svelte';
+
+    export let value = "init"
+</script>
+
+<Component>
+    <div slot="named"><Empty/></div>
+    <a href="___{value}">___{value}</a>
+</Component>