I claim the ornamental design for a storage rack fixture, as shown and described.
FIG. 1 is a top right front perspective view of a storage rack fixture showing my new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a right side elevation view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a left side elevation view thereof;
FIG. 6 is a back elevation view thereof;
FIG. 7 is a bottom plan view thereof;
FIG. 8 is a top left back perspective view thereof; and,
FIG. 9 is a reduced top right front perspective view thereof shown in use condition, the two posts and post connector shown in broken lines illustrate environmental structure only and form no part of the claimed design.