GeoModel: Work around spurious clang FPE.

There is a spot in GeoMatrial::lock that can be vectorized, but that entails executing divisions speculatively, and only checking for division by zero afterwards. This can cause problems if one is looking at FPEs. Add a dummy call in the middle of that spot to prevent vectorization.

Needed to fix failures in the FastCaloSim and MuonCombinedConfig unit tests in the clang build.