TdmsFile raises misleading FileExistsError when TDMS file path does not exist

[HasbunWoodEngineering]

When opening a TDMS file with TdmsFile, nitdms raises FileExistsError if the provided path does not exist. This is misleading, because the actual problem is that the file is missing or the relative path resolves incorrectly.

Example:

from nitdms import TdmsFile

tf = TdmsFile("missing_file.tdms")

Expected

FileNotFoundError

Actual

FileExistsError

The issue appears to come from this line:
https://github.com/l-johnston/nitdms/blob/master/nitdms/tdsapi.py#L702

Suggested Fix

if not self._file.exists():
    raise FileNotFoundError(self._file)