[mod_cgi] always set QUERY_STRING (fixes #1339)

(thx alexo)

x-ref:
  "lighttpd doesn't set empty QUERY_STRING in cgi environment"
  https://redmine.lighttpd.net/issues/1339

NEWS

@@ -63,6 +63,7 @@ NEWS
   * [stream] fstat() after open() to obtain file size
   * [core] clean up srv before exiting for lighttpd -[vVh]
   * [mod_fastcgi,mod_scgi] check for spawning on same unix socket (fixes #319)
+  * [mod_cgi] always set QUERY_STRING (fixes #1339)
 
 - 1.4.39 - 2016-01-02
   * [core] fix memset_s call (fixes #2698)

src/mod_cgi.c

@@ -956,6 +956,8 @@ static int cgi_create_env(server *srv, connection *con, plugin_data *p, buffer *
 		cgi_env_add(&env, CONST_STR_LEN("REDIRECT_STATUS"), CONST_STR_LEN("200"));
 		if (!buffer_string_is_empty(con->uri.query)) {
 			cgi_env_add(&env, CONST_STR_LEN("QUERY_STRING"), CONST_BUF_LEN(con->uri.query));
+		} else {
+			cgi_env_add(&env, CONST_STR_LEN("QUERY_STRING"), CONST_STR_LEN(""));
 		}
 		if (!buffer_string_is_empty(con->request.orig_uri)) {
 			cgi_env_add(&env, CONST_STR_LEN("REQUEST_URI"), CONST_BUF_LEN(con->request.orig_uri));