FIX: malformed <details> should not break email

plugins/discourse-details/plugin.rb

@@ -19,9 +19,14 @@ after_initialize do
 
     # replace all details with their summary in emails
     fragment.css("details").each do |details|
-      summary = details.css("summary")[0]
-      summary.name = "p"
-      details.replace(summary)
+      summary = details.css("summary")
+      if summary && summary[0]
+        summary = summary[0]
+        if summary && summary.respond_to?(:name)
+          summary.name = "p"
+          details.replace(summary)
+        end
+      end
     end
   end