qt: fix: bip70 pay reqs need x509 verification

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

- pr.verify() was called in qml, but not in qt gui
- we now call pr.verify() in get_payment_request(), to make the API less error-prone
- it is now ok to call pr.verify() multiple times, the result is cached

electrum/gui/qt/main_window.py

@@ -1438,7 +1438,7 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, Logger, QtEventListener):
             grid.addWidget(QLabel(format_time(invoice.exp + invoice.time)), 4, 1)
         if invoice.bip70:
             pr = paymentrequest.PaymentRequest(bytes.fromhex(invoice.bip70))
-            pr.verify(self.contacts)
+            pr.verify()
             grid.addWidget(QLabel(_("Requestor") + ':'), 5, 0)
             grid.addWidget(QLabel(pr.get_requestor()), 5, 1)
             grid.addWidget(QLabel(_("Signature") + ':'), 6, 0)