The ornamental design for a frame for a window or door, as shown and described.
FIG. 1 is an end elevation view of a frame for a window or door showing our new design;
FIG. 2 is a perspective view thereof;
FIG. 3 is another perspective view thereof;
FIG. 4 is another perspective view thereof; and,
FIG. 5 is another perspective view thereof.
The frame for a window or door is shown with a symbolic break line in its length. The appearance of any portion of the frame for a window or door between the jagged break lines forms no part of the claimed design.