Fix crash when open project containing a mesh with a extras dataset g…

…roups with incompatible mesh

QGis application crash when opening a project contain a mesh layer with a dataset groups wich has a incompatible mesh. It can  happen when the dataset groups file change after first loading.

src/app/mesh/qgsmeshdatasetgrouptreeview.cpp

@@ -317,7 +317,7 @@ void QgsMeshDatasetGroupTreeModel::addTreeItem( const QString &groupName, bool i
 
 QModelIndex QgsMeshDatasetGroupTreeModel::groupIndexToModelIndex( int groupIndex )
 {
-  if ( groupIndex < 0 )
+  if ( groupIndex < 0 || !mDatasetGroupIndexToItem.contains( groupIndex ) )
     return QModelIndex();
 
   const auto item = mDatasetGroupIndexToItem[groupIndex];