#20 MOOSE TreeView doesn't clear when no Model Builder is active

[Anna Wojtowicz]

Previously, the MOOSE TreeView would clear itself if no MOOSE form was active (or if the currently selected one was deleted). It no longer clears itself, causing the TreeView to throw null pointer exceptions if you futz with it after you've closed/deleted a MOOSE Model Builder.

[Jordan Deyton]

This should be fixed now.