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