Catch TypeError in indexers if content can not be adapted

Currently plone.app.discussion provides indexers
for IContentish. In these it tries to adapt
the content object to IDiscussion. But an IDiscussion Factory is only
provided for IAnnotatable.
The Criteria are IContentish but not IAnnotatable.
Indexing them fails

svn path=/plone.app.discussion/trunk/; revision=38182

plone/app/discussion/catalog.py

@@ -25,25 +25,39 @@ def total_comments(object):
     # Total number of comments on a conversation
     # Indexers won't work on old discussion items
     if object.meta_type != 'Discussion Item':
-
-        conversation = IConversation(object)
-        return conversation.total_comments
+        try:
+            conversation = IConversation(object)
+            return conversation.total_comments
+        except TypeError:
+            # The item is contentish but nobody
+            # implemented an adapter for it
+            pass
 
 @indexer(IContentish, IZCatalog)
 def last_comment_date(object):
     # Date of the latest comment on a conversation
     # Indexers won't work on old discussion items
     if object.meta_type != 'Discussion Item':
-        conversation = IConversation(object)
-        return conversation.last_comment_date
+        try:
+            conversation = IConversation(object)
+            return conversation.last_comment_date
+        except TypeError:
+            # The item is contentish but nobody
+            # implemented an adapter for it
+            pass
 
 @indexer(IContentish, IZCatalog)
 def commentators(object):
     # List of commentators on a conversation
     # Indexers won't work on old discussion items
     if object.meta_type != 'Discussion Item':
-        conversation = IConversation(object)
-        return tuple(conversation.commentators.keys())
+        try:
+            conversation = IConversation(object)
+            return tuple(conversation.commentators.keys())
+        except TypeError:
+            # The item is contentish but nobody
+            # implemented an adapter for it
+            pass
 
 # Comment Indexers