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.
diff --git a/src/http/v2/ngx_http_v2.c b/src/http/v2/ngx_http_v2.c
index a037e7a..9e24875 100644
--- a/src/http/v2/ngx_http_v2.c
+++ b/src/http/v2/ngx_http_v2.c
@@ -4039,7 +4039,7 @@
         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,