The ornamental design for a footwearliner, as shown and described.
FIG. 1 is an environmental perspective view of a footwear liner showing my new design;
FIG. 2 is an environmental top plan view thereof; and,
FIG. 3 is an environmental front elevational view thereof.
The broken line showing of a portion of the footwear liner is for illustrative purposes only, merely disclosing the types of footwear liners which may be used, and forms no part of the claimed design.