The ornamental design for a martiniglass, as shown and described.
FIG. 1 is a front perspective view of a martini glass showing my new design;
FIG. 2 is a front elevation view thereof, the left side elevation view, the right side elevation view, and the rear elevation view being identical images thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof; and,
FIG. 5 is a cross-sectional view taken on line 5-5 of FIG. 2.