qt: fix lnurl-pay

regression from https://github.com/spesmilo/electrum/pull/8462

electrum/gui/qt/send_tab.py

@@ -511,13 +511,13 @@ class SendTab(QWidget, MessageBoxMixin, Logger):
         # must not be None
         return self.amount_e.get_amount() or 0
 
-    def on_finalize_done(self, pi):
+    def on_finalize_done(self, pi: PaymentIdentifier):
         self.showSpinner(False)
         self.update_fields()
         if pi.error:
             self.show_error(pi.error)
             return
-        invoice = pi.get_invoice(self.get_amount(), self.get_message())
+        invoice = pi.bolt11
         self.pending_invoice = invoice
         self.logger.debug(f'after finalize invoice: {invoice!r}')
         self.do_pay_invoice(invoice)

electrum/payment_identifier.py

@@ -117,7 +117,7 @@ class PaymentIdentifier(Logger):
         # more than one of those may be set
         self.multiline_outputs = None
         self._is_max = False
-        self.bolt11 = None
+        self.bolt11 = None  # type: Optional[Invoice]
         self.bip21 = None
         self.spk = None
         #
@@ -406,7 +406,7 @@ class PaymentIdentifier(Logger):
             if invoice.get_amount_sat() != amount_sat:
                 raise Exception("lnurl returned invoice with wrong amount")
             # this will change what is returned by get_fields_for_GUI
-            self.bolt11 = bolt11_invoice
+            self.bolt11 = invoice
             self.set_state(PaymentIdentifierState.AVAILABLE)
         except Exception as e:
             self.error = str(e)