fix for #17187 - return NS_RDF_NO_VALUE when any particular GetTarget() calls fail

r=bienvenu

mailnews/base/src/nsMsgFolderDataSource.cpp

@@ -805,6 +805,7 @@ nsresult nsMsgFolderDataSource::createFolderNode(nsIMsgFolder* folder,
 	else if ((kNC_MessageChild == property))
 		rv = createFolderMessageNode(folder, target);
 
+  if (NS_FAILED(rv)) return NS_RDF_NO_VALUE;
   return rv;
 }
 
@@ -874,6 +875,7 @@ nsMsgFolderDataSource::createFolderServerTypeNode(nsIMsgFolder* folder,
 
   nsXPIDLCString serverType;
   rv = server->GetType(getter_Copies(serverType));
+  if (NS_FAILED(rv)) return rv;
 
   createNode(serverType, target, getRDFService());
   return NS_OK;