HTTP/2: fixed send timer handling.

Checking for return value of c->send_chain() isn't sufficient since there
are data can be left in the SSL buffer.  Now the wew->ready flag is used
instead.

In particular, this fixed a connection leak in cases when all streams were
closed, but there's still some data to be sent in the SSL buffer and the
client forgot about the connection.

src/http/v2/ngx_http_v2.c

@@ -549,7 +549,7 @@ ngx_http_v2_send_output_queue(ngx_http_v2_connection_t *h2c)
         c->tcp_nodelay = NGX_TCP_NODELAY_SET;
     }
 
-    if (cl) {
+    if (!wev->ready) {
         ngx_add_timer(wev, clcf->send_timeout);
 
     } else {