Allow empty `sapi_embedded_dir` flag in the header generator - empty `sapi_embedded_name` still disallowed
Allow empty `sapi_embedded_dir` flag in the header generator - empty `sapi_embedded_name` still disallowed

PiperOrigin-RevId: 338656398
Change-Id: Ib2ca3d63ff9bed654669d948286f73d430753a20

google/sandboxed-api,google/sandboxed-api,google/sandboxed-api,google/sandboxed-api