fix slot fallback not empty

src/compiler/compile/render_dom/Block.ts

@@ -411,8 +411,8 @@ export default class Block {
 		return body;
 	}
 
-	has_content() {
-		return this.renderer.options.dev ||
+	has_content(ignore_dev?: boolean) {
+		return (!ignore_dev && this.renderer.options.dev) ||
 			this.first ||
 			this.event_listeners.length > 0 ||
 			this.chunks.intro.length > 0 ||

src/compiler/compile/render_dom/wrappers/InlineComponent/index.ts

@@ -154,7 +154,7 @@ export default class InlineComponentWrapper extends Wrapper {
 
 		// removing empty slot
 		for (const slot of this.slots.keys()) {
-			if (!this.slots.get(slot).block.has_content()) {
+			if (!this.slots.get(slot).block.has_content(true)) {
 				this.slots.delete(slot);
 			}
 		}