HTTP/2: fixed parsing of literal header fields without indexing.

src/http/v2/ngx_http_v2.c

diff --git a/src/http/v2/ngx_http_v2.c b/src/http/v2/ngx_http_v2.c
index 9c6aeb7..54458da 100644
--- a/src/http/v2/ngx_http_v2.c
+++ b/src/http/v2/ngx_http_v2.c
@@ -1233,7 +1233,7 @@
 
     } else {
         /* literal header field without indexing */
-        prefix = ngx_http_v2_prefix(3);
+        prefix = ngx_http_v2_prefix(4);
     }
 
     value = ngx_http_v2_parse_int(h2c, &pos, end, prefix);