Eeschema: ensure the actual canvas type is saved in config.

The saved type was not updated after switching the canvas type from Preferences.

eeschema/sch_edit_frame.cpp

@@ -311,6 +311,9 @@ SCH_EDIT_FRAME::SCH_EDIT_FRAME( KIWAY* aKiway, wxWindow* aParent ) :
 
 SCH_EDIT_FRAME::~SCH_EDIT_FRAME()
 {
+    // Ensure m_canvasType is up to date, to save it in config
+    m_canvasType = GetCanvas()->GetBackend();
+
     // Shutdown all running tools
     if( m_toolManager )
     {