45 minutes in VIE is not a short connection time at all. As you're transitting Non-Schengen to Non-Schengen, just follow the signs once you're there, VIE is really easy to navigate. Till Skylink opens, it is.. 45 minutes, if your incoming flight is on time, will give you enough time to even use the lounge there. Security is at the gate unless it's a bus gate. Enjoy your travel and the great OS food ^