make the theme handling in musredit more flexible. At the same time adopted some part to more modern c++.

src/musredit_qt6/musredit/PPrefsDialog.cpp

@@ -59,6 +59,12 @@ PPrefsDialog::PPrefsDialog(PAdmin *admin) : fAdmin(admin)
     fDarkThemeIconsToolbar_checkBox->setCheckState(Qt::Unchecked);
   }
 
+  if (fAdmin->getIgnoreThemeAutoDetection()) {
+    fIgnoreThemeAutoDetection_checkBox->setCheckState(Qt::Checked);
+  } else {
+    fIgnoreThemeAutoDetection_checkBox->setCheckState(Qt::Unchecked);
+  }
+
   fKeepMn2Output_checkBox->setChecked(fAdmin->getKeepMinuit2OutputFlag());
 
   if (fAdmin->getDumpAsciiFlag() && !fAdmin->getDumpRootFlag()) {