File "electrum/gui/qt/history_list.py", line 592, in <lambda>
  File "electrum/gui/qt/main_window.py", line 3345, in bump_fee_dialog
  File "electrum/wallet.py", line 833, in bump_fee
  File "electrum/wallet.py", line 155, in get_locktime_for_new_transaction
  File "electrum/blockchain.py", line 432, in header_at_tip
  File "electrum/blockchain.py", line 182, in func_wrapper
  File "electrum/blockchain.py", line 419, in read_header
  File "electrum/blockchain.py", line 383, in assert_headers_file_available