The ornamental design for a pie crust protector, as shown and described.
FIG. 1 is a diagrammatic perspective view of the pie crust protector in full lines with lines with a person holding a pie shown in broken lines representing environmental association matter being for illustrative purposes only and forming no part of the claimed invention;
FIG. 2 is a top plan view of the pie crust protector;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a front elevational view thereof, the rear elevational view being a mirror image of the front view; and,
FIG. 5 is a right side elevational view thereof, the left side view being a mirror image of the right side view.