Boolean operation on Linux shows isValid shape, same file on Mac Does not.

[KeithSloan]

Importing from remoll geometry Mainz / detector_Mainz_v2.gdml a boolean has an invalid shape. Same file on Mac is okay. Needs further investigation i.e. check OCC versions.

[KeithSloan]

Linux Versions where the problem occurred

OS: Ubuntu 18.04.3 LTS
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.3.
Build type: Release
Python version: 3.6.8
Qt version: 5.9.5
Coin version: 4.0.0a
OCC version: 7.3.
Locale: English/UnitedKingdom (en_GB)

MacOS: macOS 10.14
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.16131 (Git)
Build type: Release
Branch: (HEAD detached at 0.18.3)
Hash: 3129ae4296e40ed20e7b3d460b86e6969acbe1c3
Python version: 3.6.7
Qt version: 5.6.2
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/UnitedKingdom (en_GB)