The ornamental design for a cover for a bicycle chainring, as shown and described.
FIG. 1 is a top, front, and left side isometric view of a cover for a bicycle chainring showing my new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a right side elevation view thereof;
FIG. 4 is a left side elevation view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is a front elevation view thereof attached to a bicycle chainring and crankarm.
The broken line showing the bicycle chainring and crankarm are provided for the purpose of illustrating environmental structure while all other broken lines illustrate portions of the cover. No subject matter shown in broken lines form part of the claimed design.