Fix dangling model pointer after reference cleanup (Fixes #1653)

apps/openmw/mwgui/companionwindow.cpp

@@ -157,6 +157,8 @@ void CompanionWindow::resetReference()
 {
     ReferenceInterface::resetReference();
     mItemView->setModel(NULL);
+    mModel = NULL;
+    mSortModel = NULL;
 }
 
 

apps/openmw/mwgui/container.cpp

@@ -262,6 +262,8 @@ namespace MWGui
     {
         ReferenceInterface::resetReference();
         mItemView->setModel(NULL);
+        mModel = NULL;
+        mSortModel = NULL;
     }
 
     void ContainerWindow::close()

apps/openmw/mwgui/tradewindow.cpp

@@ -536,5 +536,7 @@ namespace MWGui
     {
         ReferenceInterface::resetReference();
         mItemView->setModel(NULL);
+        mTradeModel = NULL;
+        mSortModel = NULL;
     }
 }