WelcomePage: fix search filter

We reduce load on the view by using beginResetModel()
and endResetModel() while filtering.

Change-Id: Id3caacc78cdba1c81d915dc1cbb40ada5bfda522
Reviewed-by: Alessandro Portale <alessandro.portale@nokia.com>

src/plugins/qtsupport/exampleslistmodel.cpp

@@ -484,7 +484,12 @@ ExamplesListModelFilter::ExamplesListModelFilter(ExamplesListModel *sourceModel,
 
 void ExamplesListModelFilter::updateFilter()
 {
-    invalidateFilter();
+    ExamplesListModel *exampleListModel = qobject_cast<ExamplesListModel*>(sourceModel());
+    if (exampleListModel) {
+        exampleListModel->beginReset();
+        invalidateFilter();
+        exampleListModel->endReset();
+    }
 }
 
 bool containsSubString(const QStringList& list, const QString& substr, Qt::CaseSensitivity cs)

src/plugins/qtsupport/exampleslistmodel.h

@@ -79,6 +79,12 @@ public:
 
     void ensureInitialized() const;
 
+    void beginReset()
+    { beginResetModel(); }
+
+    void endReset()
+    { endResetModel(); }
+
 signals:
     void tagsUpdated();