Use one loop for draft shield

src/libslic3r/GCode.cpp

@@ -4064,7 +4064,7 @@ LayerResult GCode::process_layer(
             m_avoid_crossing_perimeters.use_external_mp();
             Flow layer_skirt_flow = print.skirt_flow().with_height(float(m_skirt_done.back() - (m_skirt_done.size() == 1 ? 0. : m_skirt_done[m_skirt_done.size() - 2])));
             double mm3_per_mm = layer_skirt_flow.mm3_per_mm();
-            for (size_t i = loops.first; i < loops.second; ++i) {
+            for (size_t i = (layer.id() == 0) ? loops.first : loops.second - 1; i < loops.second; ++i) {
                 // Adjust flow according to this layer's layer height.
                 ExtrusionLoop loop = *dynamic_cast<const ExtrusionLoop*>(print.skirt().entities[i]);
                 for (ExtrusionPath &path : loop.paths) {