Split object : Check if new objects don't have a zero volume

Related to :
 * prusa3d#8931 - Split to objects crashes Prusa Slicer
 * SPE-1221(https://dev.prusa3d.com/browse/SPE-1221) - Split to objects fail

src/libslic3r/Model.cpp

@@ -1359,7 +1359,7 @@ void ModelObject::split(ModelObjectPtrs* new_objects)
         size_t counter = 1;
         for (TriangleMesh &mesh : meshes) {
             // FIXME: crashes if not satisfied
-            if (mesh.facets_count() < 3)
+            if (mesh.facets_count() < 3 || mesh.has_zero_volume())
                 continue;
 
             // XXX: this seems to be the only real usage of m_model, maybe refactor this so that it's not needed?
@@ -1833,7 +1833,7 @@ size_t ModelVolume::split(unsigned int max_extruders)
     const Vec3d offset = this->get_offset();
 
     for (TriangleMesh &mesh : meshes) {
-        if (mesh.empty())
+        if (mesh.empty() || mesh.has_zero_volume())
             // Repair may have removed unconnected triangles, thus emptying the mesh.
             continue;
 

src/libslic3r/TriangleMesh.cpp

@@ -378,6 +378,14 @@ bool TriangleMesh::is_splittable() const
     return its_is_splittable(this->its);
 }
 
+bool TriangleMesh::has_zero_volume() const
+{
+    const Vec3d sz = size();
+    const double volume_val = sz.x() * sz.y() * sz.z();
+
+    return is_approx(volume_val, 0.0);
+}
+
 std::vector<TriangleMesh> TriangleMesh::split() const
 {
     std::vector<indexed_triangle_set> itss = its_split(this->its);

src/libslic3r/TriangleMesh.hpp

@@ -139,6 +139,7 @@ class TriangleMesh
     bool   empty() const { return this->facets_count() == 0; }
     bool   repaired() const;
     bool   is_splittable() const;
+    bool   has_zero_volume() const;
     // Estimate of the memory occupied by this structure, important for keeping an eye on the Undo / Redo stack allocation.
     size_t memsize() const;