Fixes a bug where the unsigned transaction was logged by z_sendmany

after a successful sign and send, meaning that the logged hash fragment
would be different from the txid logged by "AddToWallet".  This issue
occured when sending from transparent addresses, as utxo inputs must be
signed.  It did not occur when sending from shielded addresses.

src/wallet/asyncrpcoperation_sendmany.cpp

@@ -776,6 +776,12 @@ void AsyncRPCOperation_sendmany::sign_send_raw_transaction(Object obj)
         o.push_back(Pair("hex", signedtxn));
         set_result(Value(o));
     }
+
+    // Keep the signed transaction so we can hash to the same txid
+    CDataStream stream(ParseHex(signedtxn), SER_NETWORK, PROTOCOL_VERSION);
+    CTransaction tx;
+    stream >> tx;
+    tx_ = tx;
 }