Backed out changes made to HistoryTreeWidget.cpp in revision 8289 which caused...

Backed out changes made to HistoryTreeWidget.cpp in revision 8289 which caused seg fault when importing 2 different data types. See redmine ticket #5149.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/branches/ipce@8305 41f8697f-d340-4b68-9986-7bafba869bb8