api-templates: don't show annotations block in classes if there is an empty list

Previously the block would be hidden only if the annotations property was
falsy, now it is also hidden if the property is also an empty array

public/api-builder/angular.io-package/templates/class.template.html

@@ -15,7 +15,7 @@ p.location-badge.
 {$ doc.description | indentForMarkdown(2) | trimBlankLines $}
 {% endif -%}
 
-{%- if doc.decorators %}
+{%- if doc.decorators.length %}
 .l-main-section
   h2 Annotations
 {%- for decorator in doc.decorators %}
@@ -25,10 +25,10 @@ p.location-badge.
       code.
         @{$ decorator.name $}{$ paramList(decorator.arguments) | indent(8, false) $}
 {% endfor %}
-{% endif -%}
+{%- endif %}
 
 
-{%- if doc.constructorDoc or doc.members.length -%}
+{% if doc.constructorDoc or doc.members.length -%}
 .l-main-section
   h2 Members