fix verified_tx iteration

lib/wallet.py

@@ -311,7 +311,7 @@ class Abstract_Wallet(PrintError):
         '''Used by the verifier when a reorg has happened'''
         txs = set()
         with self.lock:
-            for tx_hash, item in self.verified_tx.items():
+            for tx_hash, item in list(self.verified_tx.items()):
                 tx_height, timestamp, pos = item
                 if tx_height >= height:
                     header = blockchain.read_header(tx_height)