do not compute mass deviation using decoy proteins

src/core/identificationgroup.cpp

@@ -149,7 +149,9 @@ std::size_t IdentificationGroup::countSubGroup()const {
 void IdentificationGroup::collectMhDelta(std::vector< pappso::pappso_double> & delta_list, pappso::PrecisionUnit unit, ValidationState state) const {
     for (auto & p_protein_match : _protein_match_list) {
         if (p_protein_match->getValidationState() >= state) {
-            p_protein_match->collectMhDelta(delta_list, unit, state);
+            if (!p_protein_match->getProteinXtpSp().get()->isDecoy()) {
+                p_protein_match->collectMhDelta(delta_list, unit, state);
+            }
         }
     }
 }