logic error

[decentjohn]

If this first test fails, $is_rethemed is not yet assigned and thus throws a Tcl error.

proc retheme { pages new_theme {force 0} } {
	if { ![dui theme exists $new_theme] } {
		msg -ERROR [namespace current] retheme: "new theme '$new_theme' is not a valid theme"
		**return $is_rethemed**
	}