Don't scan documents without at least a version for duplicates.

Signed-off-by: Michael Price <loneviking72@gmail.com>

HISTORY.rst

@@ -30,6 +30,7 @@ Next (2018-XX-XX)
 - Add periodic AJAX workers to update the value of the notifications link.
 - Add notification count inside a badge on the notification link.
 - Add the MERC specifying javascript library usage.
+- Documents without at least a version are not scanned for duplicates. 
 
 2.8 (2018-02-27)
 ================

mayan/apps/documents/managers.py

@@ -116,6 +116,9 @@ class DuplicatedDocumentManager(models.Manager):
         """
         Find duplicates by matching latest version checksums
         """
+        if not document.latest_version:
+            return None
+
         Document = apps.get_model(
             app_label='documents', model_name='Document'
         )