[p3d] [assimp] assimp accepts object names with spaces, p3d doesn't
When loading a scene (e.g Blender file) with
p3d_read_blend, assimp accepts object with spaces in their names.
When creating a scenario (.sce) file from that, p3d writes instructions with that name, which is not supported by the p3d parser, when loading that scenario, hence aborting the loading of the scenario.
We should define the policy for naming objects and enforce it.