master: fix internal replication while trying to connect to upstream master

This fixes a regression in commit ad01f379
("fix leaving backup mode, including truncating to consistent TID")

neo/master/backup_app.py

@@ -299,6 +299,7 @@ class BackupApplication(object):
         result = None if primary else app.pt.setUpToDate(node, offset)
         assert cell.isReadable()
         if result: # was out-of-date
+            if primary_node is not None:
                 max_tid, = [x.backup_tid for x in cell_list
                                          if x.getNode() is primary_node]
                 if tid < max_tid: