[FIX] better handle switching user theme to 'Site default' for the 'switch_theme' module, as done before in the user preferences page.
[FIX] better handle switching user theme to 'Site default' for the 'switch_theme' module, as done before in the user preferences page.


git-svn-id: a7fabbc6a7c54ea5c67cbd16bd322330fd10cc35@8460 b456876b-0849-0410-b77d-98878d47e9d5

changi67/tiki,tikiorg/tiki,changi67/tiki,tikiorg/tiki,oregional/tiki,oregional/tiki,oregional/tiki,changi67/tiki,tikiorg/tiki,changi67/tiki,changi67/tiki,oregional/tiki,tikiorg/tiki