progs/glsl: Add missing break statement in multinoise.c.

(cherry picked from commit 43080e40aa)

progs/glsl/multinoise.c

@@ -125,6 +125,7 @@ Key(unsigned char key, int x, int y)
    case 'a':
       Anim = !Anim;
       glutIdleFunc(Anim ? Idle : NULL);
+      break;
    case 's':
       Slice -= step;
       break;