MasksSet::maskItemsQ() explicitly copy pointers

GUI/Model/Mask/MasksSet.cpp

@@ -32,7 +32,10 @@ MasksSet::~MasksSet() = default;
 
 QVector<MaskItem*> MasksSet::maskItemsQ() const
 {
-    return m_mask_items.toQVector();
+    QVector<MaskItem*> ret;
+    for (MaskItem* t : m_mask_items.toQVector())
+        ret << t;
+    return ret;
 }
 
 void MasksSet::insertMask(int row, MaskItem* maskItem)