fixed a copy/paste error.

src/musredit_qt6/musrWiz/PAdmin.cpp

@@ -535,7 +535,7 @@ bool PInstrumentDefXMLParser::startElement()
         return false;
       backward.push_back(ival);
     }
-    detect.setForwards(backward);
+    detect.setBackwards(backward);
     // detector alpha
     str = qAttr.value("alpha").toString();
     dval = str.toDouble(&ok);