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 view is identical to the front view;
FIG. 3 is a left view thereof, and the right view is identical to the left view;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof;
FIG. 6 is a perspective view of a first variant of the design;
FIG. 7 is a front view thereof and the back view is identical to the front view;
FIG. 8 is a left view thereof and the right view is identical to the left view;
FIG. 9 is a top view thereof; and,
FIG. 10 is a bottom view thereof.
The stippled lines shown throughout the drawing views are for illustrative purposes only and form no part of the claimed design. For clarity, surface shading lines are shown to illustrate contours and form no part of the design.