The ornamental design for a gamecontroller, as shown and described.
FIG. 1 is a top view of a game controller;
FIG. 2 is side view of the game controller;
FIG. 3 is a rear view of the game controller;
FIG. 4 is a front view of the game controller; and,
FIG. 5 is a bottom view of the game controller.
The broken line showing of the buttons and toggles is included for the purpose of illustrating environmental structure and forms no part of the claimed design.