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 elevational view thereof;
FIG. 6 is a left side elevational view thereof;
FIG. 7 is an enlarged front elevational view thereof; and,
FIG. 8 is an enlarged rear elevational 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.