client: fix assertion failure in case of conflict + storage disconnection

This fixes:

  Traceback (innermost last):
    ...
    Module transaction._transaction, line 393, in _commitResources
      rm.tpc_vote(self)
    Module ZODB.Connection, line 797, in tpc_vote
      s = vote(transaction)
    Module neo.client.Storage, line 95, in tpc_vote
      return self.app.tpc_vote(transaction)
    Module neo.client.app, line 546, in tpc_vote
      self.waitStoreResponses(txn_context)
    Module neo.client.app, line 539, in waitStoreResponses
      _waitAnyTransactionMessage(txn_context)
    Module neo.client.app, line 160, in _waitAnyTransactionMessage
      self._handleConflicts(txn_context)
    Module neo.client.app, line 471, in _handleConflicts
      assert oid is None, (oid, serial)
  AssertionError: ('\x00\x00\x00\x00\x00\x02\n\xe3', '\x03\xca\xad\xcb!\x92\xb6\x9c')

neo/client/transactions.py

@@ -119,6 +119,10 @@ class Transaction(object):
             if not lockless:
                 lockless = self.lockless_dict = defaultdict(set)
             lockless[app.pt.getPartition(oid)].add(uuid)
+            if oid in self.conflict_dict:
+                # In the case of a rebase, uuid_list may not contain the id
+                # of the node reporting a conflict.
+                return
         if uuid_list:
             return
         del self.data_dict[oid]
@@ -140,6 +144,9 @@ class Transaction(object):
         # with the one in `except ConnectionClosed:` clauses.
         self.conn_dict[uuid] = None
         for oid in list(self.data_dict):
+            # Exclude case of 1 conflict error immediately followed by a
+            # connection loss, possibly with lockless writes to replicas.
+            if oid not in self.conflict_dict:
                 self.written(app, uuid, oid)