The ornamental design for a portablemusicplayer, as shown and described.
FIG. 1 is a front view of a portable music player showing my design;
FIG. 2 is a back view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof; and,
FIG. 7 is a perspective view thereof.
The broken lines shown in the drawings depict portions of the portable music player in which the design is embodied that form no part of the claimed design.