KeyError in run_herg_qc if selecting a single failing well

[MichaelClerx]

To reproduce

pcpostprocess run_herg_qc tests/test_data/13112023_MW2_FF -w A01

for

INFO:root:Exporting staircaseramp (2)_2kHz as staircaseramp_2
Traceback (most recent call last):
  File "/home/michael/dev/pipeline/venv/bin/pcpostprocess", line 8, in <module>
    sys.exit(main())
             ~~~~^^
  File "/home/michael/dev/pipeline/pcpostprocess/pcpostprocess/scripts/__main__.py", line 21, in main
    run_herg_qc.main()
    ~~~~~~~~~~~~~~~~^^
  File "/home/michael/dev/pipeline/pcpostprocess/pcpostprocess/scripts/run_herg_qc.py", line 284, in main
    extract_df['selected'] = extract_df['well'].isin(overall_selection)
                             ~~~~~~~~~~^^^^^^^^
  File "/home/michael/dev/pipeline/venv/lib64/python3.13/site-packages/pandas/core/frame.py", line 4113, in __getitem__
    indexer = self.columns.get_loc(key)
  File "/home/michael/dev/pipeline/venv/lib64/python3.13/site-packages/pandas/core/indexes/range.py", line 417, in get_loc
    raise KeyError(key)
KeyError: 'well'