[k2] enable wait_queue_empty test (#1580)

Signed-off-by: Petr Shumilov <p.shumilov@vkteam.ru>

Author: PetrShumilov

tests/phpt/fork/011_queue.php

@@ -82,7 +82,8 @@ function g ($x) {
 }
 
 $res = [];
-while ($t = wait_queue_next ($q)) {
+while (!wait_queue_empty($q)) {
+  $t = wait_queue_next ($q);
   $res[] = wait($t);
 }
 sort ($res);