The ornamental design for a bladeholder, as shown and described.
FIG. 1 is a bottom perspective view of a blade holder showing my new design;
FIG. 2 is a top perspective view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a right side elevation view thereof;
FIG. 6 is a left side elevation view thereof;
FIG. 7 is a front elevation view thereof; and
FIG. 8 is a rear elevation view thereof.
The broken line showing of the blade holder attachment member is included for the purpose of illustrating environmental structure and forms no part of the claimed design.