Incorrect simulation for small mesocrystals

How to reproduce:

1. Open example with cylindrical mesocrystals
2. Reduce the outer shape dimensions, e.g. R-->2nm, H-->4nm. Each mesocrystal should contain one particle.

3. Simulate GISAS

There is no threshold effect; if the mesocrystal grows, scattering artifacts are reduced but still present and visible