do not take into account decoy proteins in grouping

src/core/proteinmatch.cpp

@@ -153,7 +153,7 @@ const std::vector<PeptideMatch *> & ProteinMatch::getPeptideMatchList() const {
 
 void ProteinMatch::setGroupingExperiment(GroupingExperiment * p_grp_experiment) {
     _sp_grp_protein = nullptr;
-    if (isValidAndChecked()) {
+    if ((isValidAndChecked() && (!_protein_sp.get()->isDecoy()))) {
         _sp_grp_protein = p_grp_experiment->getGrpProteinSp(this);
 
         for (auto & p_peptide_match : _peptide_match_list) {