Don't add null pointers for nonexistent mesh primitive data.

src/Primitives/Cube.cpp

@@ -41,6 +41,6 @@ Cube::Cube(): MeshData(Mesh::Primitive::Triangles, new vector<unsigned int>{
     Vector4( 1.0f, -1.0f,  1.0f),
     Vector4(-1.0f,  1.0f,  1.0f),
     Vector4( 1.0f,  1.0f,  1.0f)
-}}, {nullptr}, {nullptr}) {}
+}}, {}, {}) {}
 
 }}

src/Primitives/Icosphere.cpp

@@ -53,7 +53,7 @@ Icosphere<0>::Icosphere(): MeshData(Mesh::Primitive::Triangles, new vector<unsig
     Vector3(0, -0.525731f, -0.850651f),
     Vector3(0, 0.525731f, -0.850651f),
     Vector3(0, 0.525731f, 0.850651f)
-}}, {nullptr}) {
+}}, {}) {
     vertices(0)->assign(normals(0)->begin(), normals(0)->end());
 }