network: handle unparseable server-str

follow-up 9e57ae630b

fixes #6113

electrum/gui/kivy/main_window.py

@@ -150,6 +150,7 @@ class ElectrumWindow(App):
         net_params = self.network.get_parameters()
         try:
             server = ServerAddr.from_str_with_inference(server_str)
+            if not server: raise Exception("failed to parse")
         except Exception as e:
             self.show_error(_("Invalid server details: {}").format(repr(e)))
             return

electrum/gui/qt/network_dialog.py

@@ -428,6 +428,7 @@ class NetworkChoiceLayout(object):
         net_params = self.network.get_parameters()
         try:
             server = ServerAddr.from_str_with_inference(str(self.server_e.text()))
+            if not server: raise Exception("failed to parse")
         except Exception:
             return
         net_params = net_params._replace(server=server,