The ornamental design for an interiordoorpanel for an automobile, as shown and described.
FIG. 1 is a front, perspective view of an interior door panel for an automobile of my design;
FIG. 2 is a front view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a bottom view thereof;
FIG. 5 is a right side view thereof; and,
FIG. 6 is a left side view thereof.
The rear of the interior door panel is not seen during ordinary use and forms no part of the claimed design. My design includes a mirror image of the embodiment depicted.