use the default value, instead of the current one, when toggling a bo…

…olean flag, to allow for future flag duplication

vlib/flag/flag_to.v

@@ -832,6 +832,7 @@ fn keep_at_max(str string, max int) string {
 pub fn (fm FlagMapper) to_struct[T](defaults ?T) !T {
 	// Generate T result
 	mut result := defaults or { T{} }
+	the_default := defaults or { T{} }
 
 	$if T is $struct {
 		struct_name := T.name
@@ -907,7 +908,7 @@ pub fn (fm FlagMapper) to_struct[T](defaults ?T) !T {
 					if arg := f.arg {
 						return error('can not assign `${arg}` to bool field `${field.name}`')
 					}
-					result.$(field.name) = !result.$(field.name)
+					result.$(field.name) = !the_default.$(field.name)
 				} $else $if field.typ is string {
 					trace_dbg_println('${@FN}: assigning (string) ${struct_name}.${field.name} = ${f.arg or {
 						'ERROR'