When a static file larger than NXT_HTTP_STATIC_BUF_SIZE (128K) is served, two
buffers are allocated and chained; each retains the whole request memory pool.
Starting from 41331471eee7, the completion handler was called once for a linked
buffer chain, but the second buffer got lost.
This patch improves the completion handler's treatment of static buffers to
handle all linked buffers.
Max Romanov
b7dba90062