Fix crash when connecting to VNC through websocket

Connecting to VNC through websocket crashes in vnc_flush() when trying
to acquire a mutex that hasn't been initialized (vnc_init_state(vs)
hasn't been called at this point).

Signed-off-by: Jorge Acereda Macia <jacereda@gmail.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

ui/vnc-ws.c

@@ -207,8 +207,7 @@ static void vncws_send_handshake_response(VncState *vs, const char* key)
     }
 
     response = g_strdup_printf(WS_HANDSHAKE, accept);
-    vnc_write(vs, response, strlen(response));
-    vnc_flush(vs);
+    vnc_client_write_buf(vs, (const uint8_t *)response, strlen(response));
 
     g_free(accept);
     g_free(response);