An exception from a verify callback unwound through the TLS library,
which is C: OpenSSL leaked the objects of the handshake, and a server
worker thread ended the process. It also left the handshake count that
update_certs_pem() waits on raised, so with a task queue that caught the
exception, every later update waited forever. Take the exception as a
rejection, and lower the count on every way out of the handshake.