avoid errors when directly opening report concept

expert/browser/report.pt

@@ -7,7 +7,9 @@
                    renderer item/resultsRenderer"
        tal:attributes="class string:content-$level;">
     <div metal:use-macro="item/report_macros/header" />
-    <div metal:use-macro="item/resultsRenderer" />
+    <tal:renderer condition="renderer">
+      <div metal:use-macro="renderer" />
+    </tal:renderer>
   </div>
 </div>
 

expert/browser/report.py

@@ -47,6 +47,7 @@ class ReportView(ConceptView):
     """
 
     resultsRenderer = None  # to be defined by subclass
+    reportDownload = None
 
     @Lazy
     def report_macros(self):