BUG: new line at end of file causes crash

[corneliusroemer]

Having a \n at the end of a .csv or .tsv file shouldn't cause a crash.

Github for example asks for all files to end in an empty line, otherwise it will show a red stop sign.

In any case, if you want to enforce no empty lines at end, then the error should be caught and handled, before telling the user what the problem is.

How to reproduce

printf "a,b,c\n1,2,3\n\n" >a.csv
csv-diff a.csv a.csv --key a

Traceback (most recent call last):
  File "/usr/local/Caskroom/mambaforge/base/bin/csv-diff", line 8, in <module>
    sys.exit(cli())
  File "/usr/local/Caskroom/mambaforge/base/lib/python3.9/site-packages/click/core.py", line 1137, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/Caskroom/mambaforge/base/lib/python3.9/site-packages/click/core.py", line 1062, in main
    rv = self.invoke(ctx)
  File "/usr/local/Caskroom/mambaforge/base/lib/python3.9/site-packages/click/core.py", line 1404, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/Caskroom/mambaforge/base/lib/python3.9/site-packages/click/core.py", line 763, in invoke
    return __callback(*args, **kwargs)
  File "/usr/local/Caskroom/mambaforge/base/lib/python3.9/site-packages/csv_diff/cli.py", line 60, in cli
    diff = compare(load(previous), load(current), show_unchanged)
  File "/usr/local/Caskroom/mambaforge/base/lib/python3.9/site-packages/csv_diff/cli.py", line 56, in load
    return load_csv(
  File "/usr/local/Caskroom/mambaforge/base/lib/python3.9/site-packages/csv_diff/__init__.py", line 26, in load_csv
    return {keyfn(r): r for r in rows}
  File "/usr/local/Caskroom/mambaforge/base/lib/python3.9/site-packages/csv_diff/__init__.py", line 26, in <dictcomp>
    return {keyfn(r): r for r in rows}
  File "/usr/local/Caskroom/mambaforge/base/lib/python3.9/site-packages/csv_diff/__init__.py", line 21, in <lambda>
    keyfn = lambda r: r[key]
KeyError: 'a'

The error should be much better, saying which line the error is on, etc.

[raveslave]

empty lines should be skipped