Instead of an "Every tick" event, use "Is in touch" from the "Touch" object. This way the angle will only be applied when there are coordinates to apply.
When touch is not touching, Touch.X and Touch.Y are both 0, and your sprite faces this direction.
This will possibly have its own set of consequences later on (if you are having an UI for example, you will want to prevent the sprite from facing that direction when clicking/touching the button). You will likely have to refine/add conditions to your event later on depending on the rest of your game.