The ornamental design for a chainsheath, as shown and described.
FIG. 1 is a top plan view of the chain sheath;
FIG. 2 is an enlarged front perspective view of a portion of the chain sheath;
FIG. 3 is a front view of a portion of the chain sheath;
FIG. 4 is a rear view of a portion of the chain sheath;
FIG. 5 is a perspective view of an end of the chain sheath; and,
FIG. 6 is a top view of a portion of the chain sheath.
The broken lines shown in the drawings of a portion of a handbag and associated chain handle are for illustrative purposes only and form no part of the claimed design. The broken away symbols in the drawings indicate that any portion of the article beyond what is shown forms no part of the claimed design.