synchronizer: request tx from server if we only have partial local tx

Note that there is a slight distinction between
`not tx.is_complete()` and `isinstance(tx, PartialTransaction)`,
which is that technically you can have a PSBT that is already complete
but was not yet converted to a standard bitcoin tx.

electrum/synchronizer.py

@@ -30,7 +30,7 @@ import logging
 
 from aiorpcx import TaskGroup, run_in_thread, RPCError
 
-from .transaction import Transaction
+from .transaction import Transaction, PartialTransaction
 from .util import bh2u, make_aiohttp_session, NetworkJobOnDefaultServer
 from .bitcoin import address_to_scripthash, is_address
 from .network import UntrustedServerReturnedError
@@ -196,8 +196,9 @@ class Synchronizer(SynchronizerBase):
         for tx_hash, tx_height in hist:
             if tx_hash in self.requested_tx:
                 continue
-            if self.wallet.db.get_transaction(tx_hash):
-                continue
+            tx = self.wallet.db.get_transaction(tx_hash)
+            if tx and not isinstance(tx, PartialTransaction):
+                continue  # already have complete tx
             transaction_hashes.append(tx_hash)
             self.requested_tx[tx_hash] = tx_height