Reject out of context empty records

Previously if we received an empty record we just threw it away and
ignored it. Really though if we get an empty record of a different content
type to what we are expecting then that should be an error, i.e. we should
reject out of context empty records. This commit makes the necessary changes
to achieve that.

RT#4395

Reviewed-by: Andy Polyakov <appro@openssl.org>