The ornamental design for a magazine well extension, as shown and described.
FIG. 1 is an isometric view of a magazine well extension in accordance with the present disclosure;
FIG. 2 is a front elevation view of the magazine well extension of FIG. 1;
FIG. 3 is a rear elevation view of the magazine well extension of FIG. 1;
FIG. 4 is a right side elevation view of the magazine well extension of FIG. 1;
FIG. 5 is a left side elevation view of the magazine well extension of FIG. 1; and,
FIG. 6 is a top view of the magazine well extension of FIG. 1.
The broken lines in the Figures and all areas adjacent to the solid line boundaries of the claim illustrate portions of the magazine well extension that form no part of the claimed design.