qml: don't duplicate invoice (e.g. when scanned twice)

also add invoice to invoiceModel from python, not qml

electrum/gui/qml/components/WalletMainView.qml

@@ -191,10 +191,6 @@ Item {
             var dialog = lnurlPayDialog.createObject(app, { invoiceParser: invoiceParser })
             dialog.open()
         }
-
-        onInvoiceSaved: {
-            Daemon.currentWallet.invoiceModel.addInvoice(key)
-        }
     }
 
     Component {

electrum/gui/qml/qeinvoice.py

@@ -490,10 +490,14 @@ class QEInvoiceParser(QEInvoice):
         self.canSave = False
         if not self._effectiveInvoice:
             return
-        # TODO detect duplicate?
+
         self.key = self._effectiveInvoice.get_id()
-        self._wallet.wallet.save_invoice(self._effectiveInvoice)
-        self.invoiceSaved.emit(self.key)
+        if self._wallet.wallet.get_invoice(self.key):
+            self._logger.info(f'invoice {self.key} already exists')
+        else:
+            self._wallet.wallet.save_invoice(self._effectiveInvoice)
+            self._wallet.invoiceModel.addInvoice(self.key)
+            self.invoiceSaved.emit(self.key)
 
 
 class QEUserEnteredPayment(QEInvoice):