Speed up ROOT::GetFunction when the argument null

git-svn-id: http://root.cern.ch/svn/root/trunk@20796 27541ba8-7e3a-0410-8455-c3a389f83636

base/src/TROOT.cxx

@@ -882,6 +882,10 @@ TObject *TROOT::GetFunction(const char *name) const
 {
    // Return pointer to function with name.
 
+   if (name == 0 || name[0] == 0) {
+      return 0;
+   }
+
    TObject *f1 = fFunctions->FindObject(name);
    if (f1) return f1;