The ornamental design for a windowprojector, as shown and described.
FIG. 1 is a front perspective view of a window projector in accordance with the present design;
FIG. 2 is a left side view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a front view thereof;
FIG. 5 is a back view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken line showing in the figures is for the purpose of illustrating environmental structure and forms no part of the claimed design. The shading represents contour of the claimed design.