Fix mem leak found by ASAN

messageviewer/src/viewer/viewer_p.cpp

@@ -2175,8 +2175,6 @@ void ViewerPrivate::slotShowMessageSource()
     if (!mMessage) {
         return;
     }
-    mNodeHelper->messageWithExtraContent(mMessage.data());
-
     QPointer<MailSourceWebEngineViewer> viewer = new MailSourceWebEngineViewer; // deletes itself upon close
     mListMailSourceViewer.append(viewer);
     viewer->setWindowTitle(i18nc("@title:window", "Message as Plain Text"));

mimetreeparser/src/nodehelper.h

@@ -100,7 +100,7 @@ public:
     /** Return a modified message (node tree) starting from @param topLevelNode that has the original nodes and the extra nodes.
         The caller has the responsibility to delete the new message.
      */
-    KMime::Message *messageWithExtraContent(KMime::Content *topLevelNode);
+    Q_REQUIRED_RESULT KMime::Message *messageWithExtraContent(KMime::Content *topLevelNode);
 
     /** Get a QTextCodec suitable for this message part */
     const QTextCodec *codec(KMime::Content *node);