Merge remote-tracking branch 'origin/dev_native' into tm_sla_supports_backend

# Conflicts:
#	src/libslic3r/SLAPrint.hpp

src/slic3r/GUI/BackgroundSlicingProcess.cpp

@@ -294,6 +294,12 @@ void BackgroundSlicingProcess::stop_internal()
 	m_print->set_cancel_callback([](){});
 }
 
+bool BackgroundSlicingProcess::empty() const
+{
+	assert(m_print != nullptr);
+	return m_print->empty();
+}
+
 std::string BackgroundSlicingProcess::validate()
 {
 	assert(m_print != nullptr);