Userid: ngx_http_get_indexed_variable() error handling.
Userid: ngx_http_get_indexed_variable() error handling.

When evaluating a mapped $reset_uid variable in the userid filter,
if get_handler set to ngx_http_map_variable() returned an error,
this previously resulted in a NULL pointer dereference.

hy0kl/nginx,hy0kl/nginx,hy0kl/nginx