fix #1186 mouse-over heatmap may occur after heatmap has been swapped out
fix #1186 mouse-over heatmap may occur after heatmap has been swapped out

mkeilman/sirepo,mrakitin/sirepo,radiasoft/sirepo,mrakitin/sirepo,mkeilman/sirepo,radiasoft/sirepo,mkeilman/sirepo,radiasoft/sirepo,mrakitin/sirepo,mkeilman/sirepo,radiasoft/sirepo,radiasoft/sirepo,mrakitin/sirepo