Summary:
The LDB create and drop column family commands failed to check if theere was a valid database prior to dereferencing it, leading to a core dump.
The SstFileDumper prefetch code would dereference a file when the file did not exist as part of the Prefetch code. This dereference was moved inside an st.ok() check.
Tests were added for both failure conditions.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6922
Reviewed By: gg814
Differential Revision: D21884024
Pulled By: pdillinger
fbshipit-source-id: bddd45c299aa9dc7e928c17a37a96521f8c9149e
e85cbdb4e8