Fixed Joystick:isDown to accept 1-based instead of 0-based button indices

src/modules/joystick/sdl/wrap_Joystick.cpp

@@ -135,7 +135,7 @@ int w_Joystick_isDown(lua_State *L)
 
 	std::vector<int> buttons;
 	for (int i = 2; i <= lua_gettop(L); i++)
-		buttons.push_back(luaL_checkint(L, i));
+		buttons.push_back(luaL_checkint(L, i) - 1);
 
 	luax_pushboolean(L, j->isDown(buttons));
 	return 1;