Lazy init GCS client in GCS::is_empty_bucket (#1784)
Lazy init GCS client in GCS::is_empty_bucket (#1784)

The `GCS::is_empty_bucket` routine is missing a lazy init of the client, which
segfaults if it is the first used public API.
TileDB-Inc/TileDB,TileDB-Inc/TileDB,TileDB-Inc/TileDB,TileDB-Inc/TileDB