Improve several loops in GeometryPart::createMesh
Improve several loops in GeometryPart::createMesh

Remove the use of append(), and avoid repeatedly calling length().

pokyfudywise/HoudiniEngineForMaya,sideeffects/HoudiniEngineForMaya,sideeffects/HoudiniEngineForMaya,sideeffects/HoudiniEngineForMaya,pokyfudywise/HoudiniEngineForMaya,pokyfudywise/HoudiniEngineForMaya