Const'ify method + fix compile warning

src/editor/kmcomposerwin.cpp

@@ -2515,7 +2515,7 @@ void KMComposerWin::slotWordWrapToggled(bool on)
     }
 }
 
-int KMComposerWin::validateLineWrapWidth()
+int KMComposerWin::validateLineWrapWidth() const
 {
     int lineWrap = MessageComposer::MessageComposerSettings::self()->lineWrapWidth();
     if ((lineWrap == 0) || (lineWrap > 78)) {

src/editor/kmcomposerwin.h

@@ -534,8 +534,8 @@ private:
 
     void insertUrls(const QMimeData *source, const QList<QUrl> &urlList);
     void initializePluginActions();
-    Q_REQUIRED_RESULT bool showErrorMessage(KJob *job);
-    Q_REQUIRED_RESULT int validateLineWrapWidth();
+    bool showErrorMessage(KJob *job);
+    Q_REQUIRED_RESULT int validateLineWrapWidth() const;
     void slotSelectionChanged();
     void slotMessage(const QString &str);
     void slotEditorPluginInsertText(const QString &str);