Joy-1, -2, and -3 duplicate valid joysticks

[z64555]

This happens when only 1 or 2 joysticks are defined within the .cfg. Essentially the joystick with device_id of 0 is assumed to be Joy-1, -2, and -3 should any of them not be defined.

This is likely due to a bug within joy-sdl.cpp::isPlayerJoystick(). There is no signal currently to isPlayerJoystick() to determine an undefined Joystick entry, possibly because os_config_read_int().