The ornamental design for a weightliftingbar, as shown and described.
FIG. 1 is a top, front, left perspective view of a weightlifting bar showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof;
FIG. 6 is a right side view thereof; and,
FIG. 7 is a left side view thereof.
The broken lines immediately adjacent to the shaded areas define the bounds of the claimed design and form no part thereof. The broken lines depicting the remainder of the weightlifting bar show portions that form no part of the claimed design.