qt tx dialog: fix for ln-related txs when --offline

Traceback (most recent call last):
  File "/home/user/wspace/electrum/electrum/gui/qt/transaction_dialog.py", line 255, in _open_internal_link
    self.main_window.do_process_from_txid(txid=target, parent=self)
  File "/home/user/wspace/electrum/electrum/gui/qt/main_window.py", line 2212, in do_process_from_txid
    self.show_transaction(tx)
  File "/home/user/wspace/electrum/electrum/gui/qt/main_window.py", line 1079, in show_transaction
    show_transaction(tx, parent=self, desc=tx_desc)
  File "/home/user/wspace/electrum/electrum/gui/qt/transaction_dialog.py", line 351, in show_transaction
    d = TxDialog(tx, parent=parent, desc=desc, prompt_if_unsaved=prompt_if_unsaved)
  File "/home/user/wspace/electrum/electrum/gui/qt/transaction_dialog.py", line 449, in __init__
    self.update()
  File "/home/user/wspace/electrum/electrum/gui/qt/transaction_dialog.py", line 667, in update
    tx_mined_status = self.wallet.lnworker.lnwatcher.adb.get_tx_height(txid)
AttributeError: 'NoneType' object has no attribute 'adb'

electrum/gui/qt/transaction_dialog.py

@@ -664,7 +664,7 @@ class TxDialog(QDialog, MessageBoxMixin):
             item = lnworker_history[txid]
             ln_amount = item['amount_msat'] / 1000
             if amount is None:
-                tx_mined_status = self.wallet.lnworker.lnwatcher.adb.get_tx_height(txid)
+                tx_mined_status = self.wallet.adb.get_tx_height(txid)
         else:
             ln_amount = None
         self.broadcast_button.setEnabled(tx_details.can_broadcast)