qt channels_list: early exit if lightning is disabled

(note: signal is coming from a different wallet/window)

Traceback (most recent call last):
  File "...\electrum\electrum\gui\qt\channels_list.py", line 142, in do_update_single_row
    self.update_can_send(self.parent.wallet.lnworker)
  File "...\electrum\electrum\gui\qt\channels_list.py", line 164, in update_can_send
    msg = _('Can send') + ' ' + self.parent.format_amount(lnworker.can_send())\
AttributeError: 'NoneType' object has no attribute 'can_send'

electrum/gui/qt/channels_list.py

@@ -134,12 +134,15 @@ class ChannelsList(MyTreeView):
 
     @QtCore.pyqtSlot(Channel)
     def do_update_single_row(self, chan):
+        lnworker = self.parent.wallet.lnworker
+        if not lnworker:
+            return
         for row in range(self.model().rowCount()):
             item = self.model().item(row, self.Columns.NODE_ID)
             if item.data(ROLE_CHANNEL_ID) == chan.channel_id:
                 for column, v in enumerate(self.format_fields(chan)):
                     self.model().item(row, column).setData(v, QtCore.Qt.DisplayRole)
-        self.update_can_send(self.parent.wallet.lnworker)
+        self.update_can_send(lnworker)
 
     @QtCore.pyqtSlot(Abstract_Wallet)
     def do_update_rows(self, wallet):

electrum/gui/qt/main_window.py

@@ -207,7 +207,7 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, Logger):
         self.utxo_tab = self.create_utxo_tab()
         self.console_tab = self.create_console_tab()
         self.contacts_tab = self.create_contacts_tab()
-        self.channels_tab = self.create_channels_tab(wallet)
+        self.channels_tab = self.create_channels_tab()
         tabs.addTab(self.create_history_tab(), read_QIcon("tab_history.png"), _('History'))
         tabs.addTab(self.send_tab, read_QIcon("tab_send.png"), _('Send'))
         tabs.addTab(self.receive_tab, read_QIcon("tab_receive.png"), _('Receive'))
@@ -932,7 +932,7 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, Logger):
         self.channels_list.update_rows.emit(wallet)
         self.update_completions()
 
-    def create_channels_tab(self, wallet):
+    def create_channels_tab(self):
         self.channels_list = ChannelsList(self)
         t = self.channels_list.get_toolbar()
         return self.create_list_tab(self.channels_list, t)