qt: unlock wallet "OK" button bugfix

When trying to send a transaction from an encrypted wallet, the ask
passphrase dialog would not allow the user to click the "OK" button
and proceed. Therefore it was impossible to send a transaction
through the gui. It was not enabling the "OK" button after the
passphrase was entered by the user, because it was using the same
form validation logic as the "Change passphrase" flow.

src/qt/askpassphrasedialog.cpp

@@ -199,6 +199,8 @@ void AskPassphraseDialog::textChanged()
         acceptable = !ui->passEdit2->text().isEmpty() && !ui->passEdit3->text().isEmpty();
         break;
     case Unlock: // Old passphrase x1
+        acceptable = !ui->passEdit1->text().isEmpty();
+        break;
     case ChangePass: // Old passphrase x1, new passphrase x2
         acceptable = !ui->passEdit1->text().isEmpty() && !ui->passEdit2->text().isEmpty() && !ui->passEdit3->text().isEmpty();
         break;