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