HTTP/2: reject HTTP/2 requests without ":scheme" pseudo-header.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>

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 8e1b7ae..7725616 100644
--- a/src/http/v2/ngx_http_v2.c
+++ b/src/http/v2/ngx_http_v2.c
@@ -3332,6 +3332,7 @@
     static const u_char ending[] = " HTTP/2.0";
 
     if (r->method_name.len == 0
+        || r->schema_start == NULL
         || r->unparsed_uri.len == 0)
     {
         ngx_http_finalize_request(r, NGX_HTTP_BAD_REQUEST);