The ornamental design for a footstrap for a climber, as shown and described.
FIG. 1 is a perspective view of a foot strap for a climber shown attached to a wearer's foot and to a climber shown both in broken lines;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a front elevation view thereof;
FIG. 5 is a rear elevation view thereof;
FIG. 6 is a first side elevation view thereof; and,
FIG. 7 is a second side elevation view thereof.
The broken lines of a climber's foot in FIG. 1 represent unclaimed environment and form no part of the claimed design. The broken lines shown on the surface of the foot strap in FIGS. 1-3 represent thread stitching.