Always initialize m_handshakeState

The client-side constructor was leaving it uninitialized, which would
sometimes lead to spurious error signals being emitted.

Task-number: QTBUG-44893
Change-Id: I7a17f1a16d9a5fe4218beb6d92993c1889ad836b
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Liang Qi <liang.qi@theqtcompany.com>