The ornamental design for a windinstrument, as shown and described.
FIG. 1 is a perspective view of the front, top and left side of a wind instrument showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The evenly spaced broken lines illustrate the portions of the wind instrument that form no part of the claimed design. The dot-dashed broken lines represent a boundary between the claimed portions and the non-claimed portions of the design.