Marc Chevrier authored Mar 17, 2020 and Brad King committed Mar 17, 2020

In commit 3dab4682 (FindPython: reduces consumption of resources,
2020-02-10, v3.17.0-rc1~11^2) we accidentally broke the python
executable version validation when the "LOCATION" strategy is used
with the plain `FindPython` module.  Fix the logic and add test
cases covering those combinations.

Fixes: #20465