I claim the ornamental design for a lock, as shown and described.
FIG. 1 is a front left perspective view of a lock of the new design;
FIG. 2 is a front right perspective view of the lock of FIG. 1;
FIG. 3 is a front elevational view of the lock of FIG. 1;
FIG. 4 is a rear elevational view of the lock of FIG. 1;
FIG. 5 is a right side elevational view of the lock of FIG. 1;
FIG. 6 is a left side elevational view of the lock of FIG. 1;
FIG. 7 is a top plan view of the lock of FIG. 1; and,
FIG. 8 is a bottom plan view of the lock of FIG. 1.
The broken lines immediately adjacent the shaded areas represent the bounds of the claimed design while all other broken lines are directed to environment and are for illustrative purposes only; the broken lines form no part of the claimed design.