Wait for sapling activation for new addresses

src/mainwindow.cpp

@@ -1291,6 +1291,12 @@ void MainWindow::setupRecieveTab() {
             return;
 
         if (ui->rdioZSAddr->isChecked()) {
+            if (!Settings::getInstance()->isSaplingActive()) {
+                QMessageBox::critical(this, tr("Sapling not active"), 
+                        tr("Your node is still syncing, and has not synced past the sapling activation block yet. Can't create a new Sapling address until sapling is active.\n\nPlease wait for your node to sync."),
+                        QMessageBox::Ok);
+                return;
+            }
             addNewZaddr(true);
         } else if (ui->rdioTAddr->isChecked()) {
             addNewTAddr();