sort AA modifications to write the same label every time

src/core/peptidextp.cpp

@@ -52,6 +52,7 @@ const QString PeptideXtp::getModifString() const {
                 aamodif << QString::number(aa_modif->getMass(), 'f', 2);
             }
         }
+        aamodif.sort();
         QString mod_str(aamodif.join("|"));
         if (!mod_str.isEmpty()) {
             modif_list << QString("%1%2:%3").arg(i).arg(amino_acid.getLetter()).arg(mod_str);
@@ -108,4 +109,4 @@ void PeptideXtp::applyLabelingMethod(LabelingMethodSp labeling_method_sp) {
 }
 const Label * PeptideXtp::getLabel() const {
   return _p_label;
-}
\ No newline at end of file
+}