Collapse two identical if statements into a single body.

Collapse two identical if statements into a single body.

These two bodies should be grouped together anyway as the reason for
the call to BIO_flush() is to permit using BIO_set_ktls_ctrl_msg().

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Ben Kaduk <kaduk@mit.edu>
(Merged from https://github.com/openssl/openssl/pull/13090)