[#159386645] Bug fix: Crash of marquee select in dot chart when cases have been deleted
[#159386645] Bug fix: Crash of marquee select in dot chart when cases have been deleted

- Now that plotted elements are re-used, we have to check for the presence of a case in building _selectionTree

concord-consortium/codap,concord-consortium/codap,concord-consortium/codap,concord-consortium/codap,concord-consortium/codap