Fixed SetCurrentContext() assert, that was firing on closure of pcbnew, when...

Fixed SetCurrentContext() assert, that was firing on closure of pcbnew, when the OpenGL backend was active.

common/drawpanel_gal.cpp

@@ -184,6 +184,13 @@ void EDA_DRAW_PANEL_GAL::Refresh( bool eraseBackground, const wxRect* rect )
 }
 
 
+void EDA_DRAW_PANEL_GAL::StopDrawing()
+{
+    Disconnect( wxEVT_PAINT, wxPaintEventHandler( EDA_DRAW_PANEL_GAL::onPaint ), NULL, this );
+    m_refreshTimer.Stop();
+}
+
+
 void EDA_DRAW_PANEL_GAL::SwitchBackend( GalType aGalType )
 {
     // Protect from refreshing during backend switch

include/class_drawpanel_gal.h

@@ -111,6 +111,12 @@ public:
         m_eventDispatcher = aEventDispatcher;
     }
 
+    /**
+     * Function StopDrawing()
+     * Prevents the GAL canvas from further drawing till it is recreated.
+     */
+    void StopDrawing();
+
 protected:
     void onPaint( wxPaintEvent& WXUNUSED( aEvent ) );
     void onSize( wxSizeEvent& aEvent );

pcbnew/pcbframe.cpp

@@ -556,6 +556,7 @@ void PCB_EDIT_FRAME::OnQuit( wxCommandEvent& event )
 void PCB_EDIT_FRAME::OnCloseWindow( wxCloseEvent& Event )
 {
     m_canvas->SetAbortRequest( true );
+    m_galCanvas->StopDrawing();
 
     if( GetScreen()->IsModify() )
     {