The ornamental design for a handlebar, as shown and described.
FIG. 1 is a front perspective view of a handlebar;
FIG. 2 is a front elevation view of the handlebar illustrated in FIG. 1;
FIG. 3 is a rear elevation view of the handlebar illustrated in FIG. 1;
FIG. 4 is a left side elevation view of the handlebar illustrated in FIG. 1;
FIG. 5 is a right side elevation view of the handlebar illustrated in FIG. 1;
FIG. 6 is a top plan view of the handlebar illustrated in FIG. 1; and,
FIG. 7 is a bottom plan view of the handlebar illustrated in FIG. 1.
The broken lines in the drawings illustrate portions of the handlebar that form no part of the claimed design. The broken line showings of the breakaway symbols indicate continuous tubular portions of the handlebar to which are also not part of the claimed design. The dash-dot broken lines demarcate boundaries of the claimed design.