fix layer order change

src/canvas.cpp

@@ -1295,7 +1295,18 @@ void Canvas::layer_remove(int idx) // m_order index
 }
 void Canvas::layer_order(int idx, int pos) // m_order index
 {
-    std::swap(m_layers[idx], m_layers[pos]);
+    auto from = m_layers.begin() + idx;
+    auto to = m_layers.begin() + pos;
+
+    if (pos < idx)
+        std::rotate(to, from, from + 1);
+    if (pos > idx)
+        std::rotate(from, from + 1, to + 1);
+
+    if (m_current_layer_idx == idx)
+        m_current_layer_idx = pos;
+    else if (m_current_layer_idx == pos)
+        m_current_layer_idx = idx;
 }
 void Canvas::layer_merge(int source_idx, int dest_idx) // m_layer index
 {