The ornamental design for a window blind, as shown and described.
The patent or application contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
FIG. 1 is a front elevational view of a window blind showing my new design;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof;
FIG. 5 is a left side elevational view thereof; and,
FIG. 6 is a right side elevational view thereof.
The broken lines in FIGS. 3 and 4 depict portions of the window blind that form no part of the claimed design.