slightly neater locking in ngx_http_push_create_output_chain
slightly neater locking in ngx_http_push_create_output_chain

flybird119/nginx_http_push_module,h0x91b/nginx_http_push_module,lzpfmh/nginx_http_push_module,slact/nginx_http_push_module,h0x91b/nginx_http_push_module,lzpfmh/nginx_http_push_module,flybird119/nginx_http_push_module,lzpfmh/nginx_http_push_module,jedisct1/nginx_http_push_module,flybird119/nginx_http_push_module,Kronuz/nginx_http_push_module,h0x91b/nginx_http_push_module,flybird119/nginx_http_push_module,slact/nginx_http_push_module,slact/nginx_http_push_module,jedisct1/nginx_http_push_module,Kronuz/nginx_http_push_module,Kronuz/nginx_http_push_module,lzpfmh/nginx_http_push_module,slact/nginx_http_push_module,h0x91b/nginx_http_push_module,jedisct1/nginx_http_push_module