Ultraliser::Mesh segfaults on destructor

[Nadir Román Guerrero]

Ultraliser::Mesh objects built from Ultraliser::NeuronMorphology objects produce a double free on the following line:

Ultraliser/ultraliser/data/meshes/simple/MeshOptimization.cpp

Line 91 in 22128ba

 delete firstNGR; 

It can be tested by adding delete mesh; after this:

Ultraliser/ultraliser/data/volumes/Volume.cpp

Lines 510 to 511 in 22128ba

 auto mesh = new Mesh(neuronMorphology); 
 _rasterize(mesh, _grid); 

(The fact the mesh isnt being released is already a memory leak. There are futher memory leaks on the same function where this line belongs to).