Keep GLCanvas3D Building With SLIC3R_CAD Off

The bed-axes toggle added for the Design tab's reference planes reads
m_design_sketch_tool, which only exists under SLIC3R_CAD. Compute the
flag once and read the sketch tool inside the same guard as its other
uses.

src/slic3r/GUI/GLCanvas3D.cpp

@@ -2427,11 +2427,15 @@ void GLCanvas3D::_render_scene(const Camera& camera, const Size& cnv_size)
     if (m_canvas_type == ECanvasType::CanvasView3D) {
         // m_show_bed gates the plate list too: hiding the bed but leaving its grid and outline
         // floating would read as a rendering fault rather than a deliberate view option.
-        // Design tab: while its reference planes are up they draw their own axes from the modeling
-        // origin, where the bed's triad would otherwise sit on top of them.
-        if (show_bed)
-            _render_bed(camera.get_view_matrix(), camera.get_projection_matrix(), !camera.is_looking_downward(),
-                        m_show_world_axes && !(m_design_sketch_tool != nullptr && m_design_sketch_tool->draws_reference_axes()));
+        if (show_bed) {
+            bool show_axes = m_show_world_axes;
+#ifdef SLIC3R_CAD
+            // Design tab: while its reference planes are up they draw their own axes from the modeling
+            // origin, where the bed's triad would otherwise sit on top of them.
+            show_axes = show_axes && !(m_design_sketch_tool != nullptr && m_design_sketch_tool->draws_reference_axes());
+#endif
+            _render_bed(camera.get_view_matrix(), camera.get_projection_matrix(), !camera.is_looking_downward(), show_axes);
+        }
         m_frame_profiler.mark("bed");
         if (show_bed) //BBS: add outline logic
             _render_platelist(camera.get_view_matrix(), camera.get_projection_matrix(), !camera.is_looking_downward(), only_current, only_body, hover_id, true, show_grid);