The ornamental design for glass panel, as shown and described.
FIG. 1 is a perspective view of a glass panel embodying the new design; and,
FIG. 2 is a plan view thereof.
FIGS. 1 and 2 show portions of the glass panel in phantom lines. The portions shown in phantom lines form no part of the claimed design. Further, the phantom lines immediately adjacent the solid-line portions of the design form the boundary of the claimed design, with the phantom lines forming no part of the claimed design.