bug: KeyError in colrev prep

[julianprester]

Bug Report

colrev version: 0.6.0

Current behavior:

Key Error when running colrev prep

multiprocess.pool.RemoteTraceback:
"""
Traceback (most recent call last):
  File "/home/julian/.cache/pypoetry/virtualenvs/colrev-env-xI4ropgo-py3.8/lib/python3.8/site-packages/multiprocess/pool.py", line 125, in worker
    result = (True, func(*args, **kwds))
  File "/home/julian/.cache/pypoetry/virtualenvs/colrev-env-xI4ropgo-py3.8/lib/python3.8/site-packages/multiprocess/pool.py", line 48, in mapstar
    return list(map(*args))
  File "/home/julian/.cache/pypoetry/virtualenvs/colrev-env-xI4ropgo-py3.8/lib/python3.8/site-packages/pathos/helpers/mp_helper.py", line 15, in <lambda>
    func = lambda args: f(*args)
  File "/home/julian/colrev-env/colrev/colrev/ops/prep.py", line 211, in prepare
    preparation_record = endpoint.prepare(self, preparation_record)
  File "/home/julian/.cache/pypoetry/virtualenvs/colrev-env-xI4ropgo-py3.8/lib/python3.8/site-packages/timeout_decorator/timeout_decorator.py", line 92, in new_function
    return timeout_wrapper(*args, **kwargs)
  File "/home/julian/.cache/pypoetry/virtualenvs/colrev-env-xI4ropgo-py3.8/lib/python3.8/site-packages/timeout_decorator/timeout_decorator.py", line 152, in __call__
    return self.value
  File "/home/julian/.cache/pypoetry/virtualenvs/colrev-env-xI4ropgo-py3.8/lib/python3.8/site-packages/timeout_decorator/timeout_decorator.py", line 175, in value
    raise load
KeyError: 'colrev_status'
"""

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/julian/.cache/pypoetry/virtualenvs/colrev-env-xI4ropgo-py3.8/bin/colrev", line 5, in <module>
    main()
  File "/home/julian/.cache/pypoetry/virtualenvs/colrev-env-xI4ropgo-py3.8/lib/python3.8/site-packages/click/core.py", line 828, in __call__
    return self.main(*args, **kwargs)
  File "/home/julian/.cache/pypoetry/virtualenvs/colrev-env-xI4ropgo-py3.8/lib/python3.8/site-packages/click/core.py", line 781, in main
    rv = self.invoke(ctx)
  File "/home/julian/.cache/pypoetry/virtualenvs/colrev-env-xI4ropgo-py3.8/lib/python3.8/site-packages/click/core.py", line 1227, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/julian/.cache/pypoetry/virtualenvs/colrev-env-xI4ropgo-py3.8/lib/python3.8/site-packages/click/core.py", line 1046, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/julian/.cache/pypoetry/virtualenvs/colrev-env-xI4ropgo-py3.8/lib/python3.8/site-packages/click/core.py", line 590, in invoke
    return callback(*args, **kwargs)
  File "/home/julian/.cache/pypoetry/virtualenvs/colrev-env-xI4ropgo-py3.8/lib/python3.8/site-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/home/julian/colrev-env/colrev/colrev/ui_cli/cli.py", line 446, in prep
    prep_operation.main(keep_ids=keep_ids)
  File "/home/julian/colrev-env/colrev/colrev/ops/prep.py", line 734, in main
    prepared_records = pool.map(self.prepare, preparation_data)
  File "/home/julian/.cache/pypoetry/virtualenvs/colrev-env-xI4ropgo-py3.8/lib/python3.8/site-packages/pathos/multiprocessing.py", line 139, in map
    return _pool.map(star(f), zip(*args)) # chunksize
  File "/home/julian/.cache/pypoetry/virtualenvs/colrev-env-xI4ropgo-py3.8/lib/python3.8/site-packages/multiprocess/pool.py", line 364, in map
    return self._map_async(func, iterable, mapstar, chunksize).get()
  File "/home/julian/.cache/pypoetry/virtualenvs/colrev-env-xI4ropgo-py3.8/lib/python3.8/site-packages/multiprocess/pool.py", line 771, in get
    raise self._value
KeyError: 'colrev_status'

Steps to reproduce:

colrev prep