The ornamental design for a muzzleplug, as shown and described.
FIG. 1 is a front elevation view of a muzzle plug showing my new design;
FIG. 2 is a right side view thereof, the left side being a mirrored view;
FIG. 3 is a top plan view thereof;
FIG. 4 is a back elevation view thereof;
FIG. 5 is a bottom plan view thereof; and,
FIG. 6 is a front elevation view of the muzzle plug in use with a partial view of a pistol in broken lines.
The broken lines in the drawings are used to illustrate the unclaimed environment and parts of the muzzle plug, and form no part of the claimed design.