Reset fAction to allow proper re-use of TSelectorDraw (fixes <http://savannah.cern.ch/bugs/?76084>

git-svn-id: http://root.cern.ch/svn/root/trunk@37346 27541ba8-7e3a-0410-8455-c3a389f83636

tree/treeplayer/src/TSelectorDraw.cxx

@@ -108,6 +108,7 @@ void TSelectorDraw::Begin(TTree *tree)
    fSelectedRows   = 0;
    fTree = tree;
    fDimension = 0;
+   fAction = 0;
 
    const char *varexp0   = fInput->FindObject("varexp")->GetTitle();
    const char *selection = fInput->FindObject("selection")->GetTitle();