fix #1640 reset visualization beamline if deleted
fix #1640 reset visualization beamline if deleted

If the beamline used for visualization is deleted on the lattice page, reset it to use the currently selected beamline.

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