Fix Python 3 compatibility in LocatePythonModule

Regression introduced with cb345eb4bd0149b4a71d6069f957600a83cc3417.

Change-Id: I625432ac4572d2449cb6981a158e46c560a81f1a
Reviewed-on: https://code.wireshark.org/review/5883
Reviewed-by: Maarten Bezemer <maarten.bezemer@gmail.com>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>