Do not override widget visibility if already set in a layout view factory

This is particularly useful for custom layoutViewFactory setting the
widget visibility property to either true or false in a specialized
"ctkLayoutViewFactory::setupView" function. This commit will avoid
the widget visibility to be systematically forced to true by
"ctkLayoutManager::setupView".

Libs/Widgets/ctkLayoutFactory.cpp

@@ -160,8 +160,12 @@ void ctkLayoutFactory::setupView(QDomElement viewElement, QWidget* view)
   if (factory)
     {
     factory->setupView(viewElement, view);
+    d->Views.insert(view);
+    }
+  else
+    {
+    this->ctkLayoutManager::setupView(viewElement, view);
     }
-  this->ctkLayoutManager::setupView(viewElement, view);
 }
 
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