Apply suggestions from code review

Co-authored-by: Jakob Blomer <jblomer@cern.ch>

Author: hageboeck

tree/treeplayer/src/TSelectorDraw.cxx

@@ -471,8 +471,8 @@ void TSelectorDraw::Begin(TTree *tree)
    }
 
    // Decode varexp and selection
-   if (!CompileVariables(varexp.data(), realSelection.GetTitle())) {
-      abrt.Form("Variable compilation failed: {%s,%s}", varexp.data(), realSelection.GetTitle());
+   if (!CompileVariables(varexp.c_str(), realSelection.GetTitle())) {
+      abrt.Form("Variable compilation failed: {%s,%s}", varexp.c_str(), realSelection.GetTitle());
       Abort(abrt);
       return;
    }
@@ -488,7 +488,7 @@ void TSelectorDraw::Begin(TTree *tree)
    // In case fOldHistogram exists, check dimensionality
    Int_t nsel = strlen(selection);
    if (nsel > 1) {
-      htitle.Form("%s {%s}", varexp.data(), selection);
+      htitle.Form("%s {%s}", varexp.c_str(), selection);
    } else {
       htitle = varexp;
    }