Summary:
`dbs` should not be cleared, as it is reused later when reopening the DBs, so we have an out-of-bounds access with `dbnames[dbnum]`. The values left in the vector don't need to be reset, as the db pointer is an out parameter for `DB::Open`.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9046

Reviewed By: pdillinger

Differential Revision: D31738263

Pulled By: ot

fbshipit-source-id: c619e947b8d3dbc3d896f29971f093d3e3c794d3