We claim the ornamental design for a lock, as shown and described.
FIG. 1 is a perspective view of a lock made in accordance with an embodiment of the new design;
FIG. 2 is a front view of the lock of FIG. 1;
FIG. 3 is a rear view of the lock of FIG. 1;
FIG. 4 is a side view of the lock of FIG. 1, the opposite side being a mirror image of FIG. 4;
FIG. 5 is a top view of the lock of FIG. 1; and,
FIG. 6 is a bottom view of the lock of FIG. 1.
The portions of the Figures shown in phantom lines are not part of the claimed design but are for either illustration only, or to define the boundaries of the claimed design.