Ext.grid.plugin.SelectionSubmit error while destroying instance with SpreadsheetModel

[fabriciomurta]

Found: 4.2.0
Ext.NET forum thread: Change Selection Model of GridPanel

On Ext.NET 4.1.0, while destroying an Ext.grid.plugin.SelectionSubmit, at least in the test case provided with the thread above, the selection model was always null.

As of Ext.NET 4.2.0, it is not and the code override handling the destruction of the class instance was mistakenly trying to reference the grid from the selection model, while it should have been done from the own Ext.grid.plugin.SelectionSubmit instance.