qt: disable ln configs in ConfirmTxDialog if no ln

Disables the lightning related config options in the ConfirmTxDialog
tools and shows an according tooltip if lightning is not available in
the wallet. This should prevent confusion of users.

electrum/gui/qt/confirm_tx_dialog.py

@@ -500,8 +500,23 @@ class TxEditor(WindowModalDialog, QtEventListener, Logger):
             self.resize_to_fit_content()
         self.pref_menu.addConfig(self.config.cv.GUI_QT_TX_EDITOR_SHOW_LOCKTIME, callback=cb)
         self.pref_menu.addSeparator()
-        self.pref_menu.addConfig(self.config.cv.WALLET_SEND_CHANGE_TO_LIGHTNING, callback=self.trigger_update)
-        self.pref_menu.addConfig(self.config.cv.WALLET_ENABLE_SUBMARINE_PAYMENTS, callback=self.update_tab_visibility)
+        can_have_lightning = self.wallet.can_have_lightning()
+        send_ch_to_ln = self.pref_menu.addConfig(
+            self.config.cv.WALLET_SEND_CHANGE_TO_LIGHTNING,
+            callback=self.trigger_update,
+            checked=False if not can_have_lightning else None,
+        )
+        sub_payments = self.pref_menu.addConfig(
+            self.config.cv.WALLET_ENABLE_SUBMARINE_PAYMENTS,
+            callback=self.update_tab_visibility,
+            checked=False if not can_have_lightning else None,
+        )
+        if not can_have_lightning:  # disable the buttons and override tooltip
+            ln_unavailable_msg = _("Not available for this wallet.") \
+                                 + "\n" + _("Requires a wallet with Lightning network support.")
+            for ln_conf in (send_ch_to_ln, sub_payments):
+                ln_conf.setEnabled(False)
+                ln_conf.setToolTip(ln_unavailable_msg)
         self.pref_menu.addToggle(
             _('Use change addresses'),
             self.toggle_use_change,