Throw a more useful error message if no logs were parsed

[simonbowly]

If the glob pattern matches no files (which can easily happen due to a typo, or being in the wrong directory), we get this unhelpful error during post-processing:

>>> import grblogtools as glt
>>> glt.parse("asdjkhaskd")
<grblogtools.api.ParseResult object at 0x1023f75b0>
>>> glt.parse("asdjkhaskd").summary()
Traceback (most recent call last):
  File "/Users/bowly/.pyenv/versions/3.10.3/lib/python3.10/site-packages/pandas/core/indexes/base.py", line 3800, in get_loc
    return self._engine.get_loc(casted_key)
  File "pandas/_libs/index.pyx", line 138, in pandas._libs.index.IndexEngine.get_loc
  File "pandas/_libs/index.pyx", line 165, in pandas._libs.index.IndexEngine.get_loc
  File "pandas/_libs/hashtable_class_helper.pxi", line 5745, in pandas._libs.hashtable.PyObjectHashTable.get_item
  File "pandas/_libs/hashtable_class_helper.pxi", line 5753, in pandas._libs.hashtable.PyObjectHashTable.get_item
KeyError: 'Version'

We should throw something more useful, like a FileNotFoundError at the parsing step if no files match.