The ornamental design for a petcomb, as shown and described.
FIG. 1 is a top perspective view of the present pet comb;
FIG. 2 is a left side view of same;
FIG. 3 is a right side view of the pet comb of FIG. 1;
FIG. 4 is a top plan view of same;
FIG. 5 is a bottom view of the pet comb of FIG. 1;
FIG. 6 is a rear view of same; and,
FIG. 7 is a front view of the pet comb of FIG. 1.
The subject matter shown in broken lines is submitted for disclosing the environment of the claimed design, and forms no part of the claimed subject matter.