Move logic out of thumbnail component template and into the class (#3639)

Author: jcoyne

app/components/blacklight/document/thumbnail_component.html.erb

@@ -1,7 +1,3 @@
-<% value = presenter.thumbnail.render(@image_options) %>
-
-<% if value %>
-  <div class="document-thumbnail">
-    <%= helpers.link_to_document(presenter.document, value, 'aria-hidden': true, tabindex: -1, counter: @counter) %>
-  </div>
-<% end %>
+<div class="document-thumbnail">
+  <%= helpers.link_to_document(presenter.document, thumbnail_value, 'aria-hidden': true, tabindex: -1, counter: @counter) %>
+</div>

app/components/blacklight/document/thumbnail_component.rb

@@ -17,8 +17,12 @@ def initialize(counter:, presenter: nil, image_options: {})
 
       attr_accessor :presenter
 
+      def thumbnail_value
+        @thumbnail_value ||= presenter.thumbnail.render(@image_options)
+      end
+
       def render?
-        presenter.thumbnail.exists?
+        presenter.thumbnail && thumbnail_value
       end
     end
   end