HTTP/2: improved handling of preread unbuffered requests.

Previously, fully preread unbuffered requests larger than client body
buffer size were saved to disk, despite the fact that "unbuffered" is
expected to imply no disk buffering.

src/http/v2/ngx_http_v2.c

@@ -4039,7 +4039,7 @@ ngx_http_v2_read_request_body(ngx_http_request_t *r)
         len++;
     }
 
-    if (r->request_body_no_buffering && !stream->in_closed) {
+    if (r->request_body_no_buffering) {
 
         /*
          * We need a room to store data up to the stream's initial window size,