The ornamental design for a lightfixture, as shown and described.
FIG. 1 is a perspective view of a light fixture in accordance with my design;
FIG. 2 is a top plan view of the light fixture in accordance with my design;
FIG. 3 is a bottom plan view of the light fixture in accordance with my design;
FIG. 4 is a right-side elevation view of the light fixture; and,
FIG. 5 is a left-elevation view of the light fixture. The broken-line disclosure of elements is understood to represent portions of the article in which the design is embodied, but which form no part of the claimed design.