The ornamental design for a wirelesscharger, as shown and described.
FIG. 1 is a perspective view of a wireless charger showing my design;
FIG. 2 is a front view thereof;
FIG. 3 is a back view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The dashed broken lines in the drawings depict portions of the wireless charger that form no part of the claimed design. The dash-dot broken lines define the boundaries of the claim that form no part of the claim.