The ornamental design for a magnifier, as shown and described.
FIG. 1 is a perspective view of a magnifier showing our new design;
FIG. 2 is a top plan view of FIG. 1;
FIG. 3 is a right side elevational view of FIG. 1;
FIG. 4 is a left side elevational view of FIG. 1;
FIG. 5 is a bottom plan view of FIG. 1;
FIG. 6 is a first end elevational view of FIG. 1; and,
FIG. 7 is a second end elevational view of FIG. 1.
The dotted lines are intended to show features that are environmental only and form no part of the claimed design. Also, there is no intent to claim any surface indicia as all such surface lines are merely intended to be shading lines.