(def) Prevent computation for too small mesh

DDicretization now throws a runtime error if the mesh size is < 2 elements.

blast/src/DDiscretization.cpp

@@ -17,6 +17,8 @@ void Discretization::setGlob(std::vector<double> &_x, std::vector<double> &_y, s
 {
     if (_x.size() != _y.size() || _y.size() != _z.size() || _x.size() != _z.size())
         throw std::runtime_error("blast::Discretization Wrong mesh sizes.\n");
+    if (_x.size() < 2 || _y.size() < 2 || _z.size() < 2)
+        throw std::runtime_error("blast::Discretization Mesh too small.\n");
 
     nMarkers = _x.size();
     x.resize(nMarkers, 0.);