The ornamental design for a mug handle, as shown and described.
FIG. 1 is a perspective view of the mug handle showing the design, with a mug illustrated in dashed lines to illustrate one example of the mug handle in context;
FIG. 2 is a side view of the mug handle illustrated in FIG. 1, again showing a mug in dashed lines to illustrate one example of the mug handle in context;
FIG. 3 is an opposite side view of the mug handle thereof;
FIG. 4 is a rear view of the mug handle thereof;
FIG. 5 is a top view of the mug handle thereof; and,
FIG. 6 is a bottom view of the mug handle thereof.
The broken lines represents an exemplary environment in which the article resides form no part of the claim.