The ornamental design for a tabletcomputer protective casing, as shown and described.
FIG. 1 is a front right side top perspective view of the tablet computer protective casing showing my new design;
FIG. 2 is an inverted left side top perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof.
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a right side elevational view thereof;
FIG. 7 is a top plan view thereof;
FIG. 8 is a bottom plan view thereof; and,
FIG. 9 is rear perspective view thereof showing a support component extended from the rear surface of the tablet computer protective casing so as to support the tablet computer protective casing in a tilted mode upon a support surface.
The broken lines represent portions of the structure that form no part of the claim.