The ornamental design for a flap for a garment, as shown and described.
FIG. 1 is a right side view of a flap for a garment showing my new design in the closed condition, the opposite side being a mirror image;
FIG. 2 is a rear perspective view thereof, shown in the closed condition;
FIG. 3 is a right side view thereof, shown in an open condition, the opposite side being a mirror image thereof; and,
FIG. 4 is a rear perspective view thereof, shown in the open condition.
In all of the figures, the claimed design being represented inside the unbroken solid lines and the broken lines partially showing a garment are for illustrative purposes only and form no part of the claimed design.