The 50 cent small blind was a forced bet and when the SB folds before putting any voluntary money into the pot he will have a 0% VPIP. Now players new to the concept may be confused because the SB did put money into the pot with his 50 cent blind, but remember, the key part of VPIP is the voluntarily aspect. The button folds, giving him a 0% VPIP and the SB folds as well.
