The ornamental design for a portion of a handle for a bag, as shown and described.
FIG. 1 is a front perspective view of a portion of a handle for a bag showing my new design;
FIG. 2 is a front view of the portion of a handle for a bag shown in FIG. 1;
FIG. 3 is a side view of the portion of a handle for a bag shown in FIG. 1 (with the other side view being a mirror image thereof); and,
FIG. 4 is a top view of the portion of a handle for a bag shown in FIG. 1.
The broken line showing of the handles, portions of the handbag, and central closure mechanism is for illustrative purposes only and forms no part of the claimed design.