Avoid closing the color toolbar also via (e.g. Alt-F4) shortcut

BUG: 456919

widgets/toolbars/kpColorToolBar.h

@@ -32,7 +32,7 @@
 
 #include <QDockWidget>
 #include <QFrame>
-#include <QWidget>
+#include <QCloseEvent>
 
 #include "imagelib/kpColor.h"
 
@@ -111,6 +111,8 @@ protected:
     void dragEnterEvent (QDragEnterEvent *e) override;
     void dragMoveEvent (QDragMoveEvent *e) override;
 
+    void closeEvent(QCloseEvent *event) override { event->ignore(); }
+
 private:
     void adjustToOrientation (Qt::Orientation o);