Fix slot fallback

Author: tronsha

tests/fixtures/vue-slot/component-has-two-default-slots-with-fallback-value.twig

@@ -8,4 +8,4 @@
 <button class="{{ class|default('') }}" style="{{ style|default('') }}">
     {{ slot_default|default(slot_default_fallback_2) }}
 </button>
-{% endif %}
+{% endif %}