As the charge is "found in or leaving after having been in a place, that provides unlawful prostitution", technically that's the only thing they need to prove. You don't need to be busted in the act. If you were then they could throw another charge at you for "partaking in illegal prostitution".
In saying all that, the question I was answering asked if it was illegal just to be in a shop and if you can be arrested for just being there. Mud sticks, so depending on your employer, if they found out you had to go to court for this, it could potentially do damage to your working career, whether you were found guilty or not.