Reproduction steps:

1. In pkg/storage/engine/tee.go, change GetStats and PreIngestDelay to call into eng1 (rocksdb) instead of eng2 (usually pebble).
2. Run COCKROACH_STORAGE_ENGINE=pebble+rocksdb make test PKG=./pkg/storage/engine/...
3. Observe TestDBAddSSTable (and some other tests) crash with a segfault in GetStats.

When RocksDB is used directly (i.e. with the COCKROACH_STORAGE_ENGINE=rocksdb env variable or with that env variable unset), the same tests pass. This issue could be due to an interaction with Pebble, or with the way the teeing engine starts up RocksDB.