Prevent an infinite recursion when the query cache is flushed.

Prevent an infinite recursion when the query cache is flushed.

The problem being that the "requires flush" flag was being cleared after the
the flush.  The fix is to clear it before.  This is a problem because the
cache flushing called RAND_bytes and if the DRBG hadn't been created yet, it
would be queried and added to the cache causing the flush code to repeat.

Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/9477)