The ornamental design for a portabledesk, as shown and described.
FIG. 1 is a front perspective view of a portable desk showing my new
design;
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a rear perspective view with the extendable support arm in
position of use; the broken line showing of a chair is for illustrative
purposes only and forms no part of the claimed design; and