The ornamental design for a bulbholder, as shown and described.
FIG. 1 is a perspective view of a bulb holder showing our new design;
FIG. 2 is a front view thereof, and the back, left and right views are identical to the front view;
FIG. 3 is a top view thereof; and,
FIG. 4 is a bottom view thereof.
The broken lines shown in the drawings are included for the purpose of illustrating portions of the bulb holder that form no part of the claimed design.