Unhandled game controller button events cause a panic

[potatotech]

SDL2 has some undocumented button types for game controllers.
Currently, these are:

SDL_CONTROLLER_BUTTON_MISC1
SDL_CONTROLLER_BUTTON_PADDLE1
SDL_CONTROLLER_BUTTON_PADDLE2
SDL_CONTROLLER_BUTTON_PADDLE3
SDL_CONTROLLER_BUTTON_PADDLE4
SDL_CONTROLLER_BUTTON_TOUCHPAD

Although they are present in the automatically-generated bindings, they have no defined equivalent in the safe bindings.

When these button events appear, the following line causes a panic:

rust-sdl2/src/sdl2/controller.rs

Line 333 in c4f31c6

_ => panic!("unhandled controller button"),

This is the root cause of #1128.

[Cobrand]

Yeah panicking it a terrible idea, just return None in those cases (or better: implement them). It's not really a bug since it's expected, but it should be fixed nonetheless.