I claim the ornamental design for a diffuser, as shown and described.
FIG. 1 is a front left top perspective view of the diffuser;
FIG. 2 is a rear right top perspective view of the diffuser;
FIG. 3 is a front right bottom perspective view of the diffuser;
FIG. 4 is a front view of the diffuser;
FIG. 5 is a rear view of the diffuser;
FIG. 6 is a left side view of the diffuser;
FIG. 7 is a right side view of the diffuser;
FIG. 8 is a top view of the diffuser; and,
FIG. 9 is a bottom view of the diffuser.
The broken lines in the FIGURES depict portions of the diffuser that form no part of the claimed design. The unshaded surfaces bounded by broken lines form no part of the claimed design.