The ornamental design for a pull cordpositioningdevice for a windowcurtain, as shown and described.
FIG. 1 is a perspective view of a pull cord positioning device for a window curtain;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a rear perspective view of the device and shows the device being mounted on a wall and a pull cord being installed in the device, the broken line forming the pull cord and the wall forming no part of the claim.