The ornamental design for the eyelash guard, as shown and described.
FIG. 1 is a front elevation view of the eyelash guard thereof;
FIG. 2 is a left side view of the eyelash guard thereof, a right side view being identical to the left side view;
FIG. 3 is a rear elevation view of the eyelash guard thereof;
FIG. 4 is a top plan view of the eyelash guard thereof;
FIG. 5 is a bottom plan view of the eyelash guard, thereof;
FIG. 6 is a front elevational view of the middle element of the eyelash guard shown separately for convenience of illustration, the rear elevational view being identical to the front view;
FIG. 7 is a left side elevational view of the middle element of the eyelash guard shown separately for convenience of illustration, the right side elevational view being identical to the front view; and,
FIG. 8 is a top plan view of the middle element of the eyelash guard shown separately for convenience of illustration, the bottom plan view being identical to the front view.