The ornamental design for a ladderstabilizer, as shown and described.
FIG. 1 is a front perspective view of a ladder stabilizer showing our new design:
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a front elevational view thereof;
FIG. 5 is a right side elevational view thereof, of which the left side elevational view is a mirror image of FIG. 5;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines shown in the figures are included for the purposes of illustrating portions of the ladder stabilizer that form no part of the claimed design.