Don't fail on missing file

[delucchi-cmu]

In this case, the benchmarks were not set up yet on the repo, and I think it would be preferable to just pass through and not fail to create a new table from the file.

Traceback (most recent call last):
  File "/usr/lib/python3.10/runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/lib/python3.10/runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "/home/runner/.local/lib/python3.10/site-packages/lf_asv_formatter/__main__.py", line 115, in <module>
    headers, rows = format_asv_table_from_file(output_file)
  File "/home/runner/.local/lib/python3.10/site-packages/lf_asv_formatter/__main__.py", line 54, in format_asv_table_from_file
    headers = format_headers(rows[0])
IndexError: list index out of range