Fix msan error introduced in https://github.com/openxla/xla/commit/7b4b2754f96309dd76d0ecbea12c2e9b5533f74d.
Fix msan error introduced in https://github.com/openxla/xla/commit/7b4b2754f96309dd76d0ecbea12c2e9b5533f74d.

The commit above makes accessing args.attributes unconditionally when creating a PJRT C API client.
