prevents repeated generation of the same kd-tree

...GridGenerator/geometries/TriangularMesh/TriangularMesh.cu

src/GridGenerator/geometries/TriangularMesh/TriangularMesh.h

...ator/geometries/TriangularMesh/TriangularMeshStrategy.cpp

...rtualFluidsBasics/numerics/geometry3d/GbTriFaceMesh3D.cpp

src/VirtualFluids_GPU/Calculation/UpdateGrid27.cpp

targets/apps/HULC/main.cpp