Merge bitcoin-core/gui#653: Show watchonly balance only for Legacy wallets

fdb8dc8 gui: Show watchonly balance only for Legacy wallets (Andrew Chow)

Pull request description:

  Descriptor wallets do not have a watchonly balance as wallets are designated watchonly or not. Thus we should not be displaying the empty watchonly balance for descriptor wallets.

  The result is that instead of the send page showing "Watch-only balance: 0.00000000 BTC" for watchonly descriptor wallets, we see the actual balance as "Balance: 10.00000000 BTC"

ACKs for top commit:
  johnny9:
    tACK fdb8dc8
  furszy:
    ACK fdb8dc8
  hebasto:
    ACK fdb8dc8

Tree-SHA512: e5c0703a62d25c881c8dadfb9cffd482791f3d437a4ec5ae0088ce1a2069c2455ad6d3ec6c95a4404a3b55fbd727f92694529c35052236951553ca90c4ed31b5

Author: hebasto

src/qt/sendcoinsdialog.cpp

@@ -699,7 +699,7 @@ void SendCoinsDialog::setBalance(const interfaces::WalletBalances& balances)
         CAmount balance = balances.balance;
         if (model->wallet().hasExternalSigner()) {
             ui->labelBalanceName->setText(tr("External balance:"));
-        } else if (model->wallet().privateKeysDisabled()) {
+        } else if (model->wallet().isLegacy() && model->wallet().privateKeysDisabled()) {
             balance = balances.watch_only_balance;
             ui->labelBalanceName->setText(tr("Watch-only balance:"));
         }