The ornamental design for a portable shadestructure, as shown and described.
FIG. 1 shows a front elevational view of the portable shade structure showing my new design;
FIG. 2 shows a side elevational view thereof;
FIG. 3 shows a perspective view thereof; and,
FIG. 4 shows a perspective view thereof with a shade cover attached, it being understood that the attached shade cover is for illustrative purposes only to show the environment in which the claimed design is used, the shade forming no part of the claimed design.
Portions of the claimed design are shown separated using line breaks to indicate indeterminate length.