Fix error where a temp directory leads to an error
Fix error where a temp directory leads to an error

With "-t TMPDIR" set, the Python code yields a LocalPath object using
plumbum - which evidently breaks the existing 'os.path.exists' check.

This patch converts the LocalPath object to a String, as seen in other
places of the code.

Signed-off-by: Claus Hunsen <hunsen@fim.uni-passau.de>

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