The data pointer in ngx_open_file_t objects must be initialized.

Uninitialized pointer may result in arbitrary segfaults if access_log is used
without buffer and without variables in file path.

Patch by Tatsuhiko Kubo (ticket #268).

src/core/ngx_conf_file.c

@@ -946,6 +946,7 @@ ngx_conf_open_file(ngx_cycle_t *cycle, ngx_str_t *name)
     }
 
     file->flush = NULL;
+    file->data = NULL;
 
     return file;
 }