better move semantics use in rvalue_ref

alib2std/src/extensions/utility.hpp

@@ -71,11 +71,11 @@ struct rvalue_ref {
 		delete holder;
 	}
-	T * operator ->( ) {
+	T * operator ->( ) && {
 		return holder;
 	}
-	T * operator ->( ) const {
+	T * operator ->( ) const & {
 		return holder;
 	}