Fix document template column field.

GitLab issue #655. Thanks to Christian Wiegand (@christianwgd) for the
report.

Signed-off-by: Roberto Rosario <Roberto.Rosario@mayan-edms.com>

mayan/apps/document_indexing/apps.py

@@ -135,8 +135,8 @@ class DocumentIndexingApp(MayanAppConfig):
             widget=TwoStateWidget
         )
         SourceColumn(
-            attribute='enabled', is_sortable=True, source=IndexTemplateNode,
-            widget=TwoStateWidget
+            attribute='link_documents', is_sortable=True,
+            source=IndexTemplateNode, widget=TwoStateWidget
         )
         SourceColumn(
             func=lambda context: index_instance_item_link(context['object']),