The ornamental design for a facemaskextender, as shown and described.
FIG. 1 is a perspective view of the face mask extender.
FIG. 2 is front view thereof.
FIG. 3 is a back perspective view thereof.
FIG. 4 is left side view thereof.
FIG. 5 is right side view thereof.
FIG. 6 is top view thereof; and,
FIG. 7 is bottom view thereof.
The broken lines showing the equidistantly aligned, circular features with an inner ornament, as shown in FIGS. 1 and 2 illustrate environmental features that form no part of the claimed design.