update color at picking and cleanup code from some warnings

src/node_panel_grid.cpp

@@ -414,7 +414,7 @@ void NodePanelGrid::bake_uvs()
         {
             for (int x = 0; x < fb.getWidth(); x++)
             {
-                int i = y * fb.getHeight() + x;
+                int i = (int)y * fb.getHeight() + x;
                 auto nor = glm::make_vec3(&d_nor[i * 4]);
                 auto pos = glm::make_vec3(&d_pos[i * 4]);
                 auto& out = d_out[i];