Manual merge of the TriangleMesh.cpp from the stable branch.

src/libslic3r/SLAPrint.hpp

@@ -185,6 +185,7 @@ public:
     bool                empty() const override { return m_objects.empty(); }
     ApplyStatus         apply(const Model &model, const DynamicPrintConfig &config) override;
     void                process() override;
+    // Returns true if an object step is done on all objects and there's at least one object.    
     bool                is_step_done(SLAPrintObjectStep step) const;
     // Returns true if the last step was finished with success.
     bool                finished() const override { return this->is_step_done(slaposIndexSlices); }