wallet.py: access unverified_tx with self.lock

Only actually needed due to Imported_Wallet.delete_address, but it takes some time to see this.
The verifier and the synchronizer both access unverified_tx but they are both run in the Network thread.
In any case, there does not seem to be a measurable performance hit when using the lock.

lib/wallet.py

@@ -205,11 +205,9 @@ class Abstract_Wallet(PrintError):
         self.fiat_value            = storage.get('fiat_value', {})
         self.receive_requests      = storage.get('payment_requests', {})
 
-        # Verified transactions.  Each value is a (height, timestamp, block_pos) tuple.  Access with self.lock.
+        # Verified transactions.  txid -> (height, timestamp, block_pos).  Access with self.lock.
         self.verified_tx = storage.get('verified_tx3', {})
-
-        # Transactions pending verification.  A map from tx hash to transaction
-        # height.  Access is not contended so no lock is needed.
+        # Transactions pending verification.  txid -> tx_height. Access with self.lock.
         self.unverified_tx = defaultdict(int)
 
         self.load_keystore()
@@ -460,19 +458,21 @@ class Abstract_Wallet(PrintError):
 
         # tx will be verified only if height > 0
         if tx_hash not in self.verified_tx:
-            self.unverified_tx[tx_hash] = tx_height
+            with self.lock:
+                self.unverified_tx[tx_hash] = tx_height
 
     def add_verified_tx(self, tx_hash, info):
-        # Remove from the unverified map and add to the verified map and
-        self.unverified_tx.pop(tx_hash, None)
+        # Remove from the unverified map and add to the verified map
         with self.lock:
+            self.unverified_tx.pop(tx_hash, None)
             self.verified_tx[tx_hash] = info  # (tx_height, timestamp, pos)
         height, conf, timestamp = self.get_tx_height(tx_hash)
         self.network.trigger_callback('verified', tx_hash, height, conf, timestamp)
 
     def get_unverified_txs(self):
         '''Returns a map from tx hash to transaction height'''
-        return self.unverified_tx
+        with self.lock:
+            return dict(self.unverified_tx)  # copy
 
     def undo_verifications(self, blockchain, height):
         '''Used by the verifier when a reorg has happened'''