Fix drawing background before drawing toolbar bitmap

The Cairo origin is already set up for the widget

src/gtk/toolbar.cpp

@@ -196,7 +196,7 @@ image_expose_event(GtkWidget* widget, GdkEventExpose*, wxToolBarTool* tool)
     int y = (alloc.height - bitmap.GetScaledHeight()) / 2;
 #ifdef __WXGTK3__
     gtk_render_background(gtk_widget_get_style_context(widget),
-        cr, alloc.x, alloc.y, alloc.width, alloc.height);
+        cr, 0, 0, alloc.width, alloc.height);
     bitmap.Draw(cr, x, y);
 #else
     x += alloc.x;