The ornamental design for a wound dressing, as shown and described.
FIG. 1 is a top perspective view of a wound dressing in a position of use;
FIG. 2 is another top perspective view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a bottom view thereof;
FIG. 5 is an end view thereof;
FIG. 6 is a side view thereof; and,
FIG. 7 is another side view thereof.
The broken lines showing of a human arm in FIG. 1 and the broken line showing of threading in FIGS. 1, 3, 4, 5, 6 and 7 are for the purpose of illustrating environment and form no part of the claimed design. The broken line illustrating a stripe pattern on the wound dressing is for the purpose of illustrating portions of a wound dressing and forms no part of the claim.