Fix SDL_GAMECONTROLLER handling

1. Do not disable SDL_JOYSTICK events. Disabling these events causes
   game controller events to be disabled as well. Instead, filter these events out.

2. Fix button mapping (it was off by one).

engine/platform/sdl/events.c

@@ -390,19 +390,23 @@ static void SDLash_EventFilter( SDL_Event *event )
 
 	/* Joystick events */
 	case SDL_JOYAXISMOTION:
+		if ( SDL_GameControllerFromInstanceID( event->jaxis.which ) == NULL )
 			Joy_AxisMotionEvent( event->jaxis.axis, event->jaxis.value );
 		break;
 
 	case SDL_JOYBALLMOTION:
+		if ( SDL_GameControllerFromInstanceID( event->jball.which ) == NULL )
 			Joy_BallMotionEvent( event->jball.ball, event->jball.xrel, event->jball.yrel );
 		break;
 
 	case SDL_JOYHATMOTION:
+		if ( SDL_GameControllerFromInstanceID( event->jhat.which ) == NULL )
 			Joy_HatMotionEvent( event->jhat.hat, event->jhat.value );
 		break;
 
 	case SDL_JOYBUTTONDOWN:
 	case SDL_JOYBUTTONUP:
+		if ( SDL_GameControllerFromInstanceID( event->jbutton.which ) == NULL )
 			Joy_ButtonEvent( event->jbutton.button, event->jbutton.state );
 		break;
 
@@ -514,7 +518,7 @@ static void SDLash_EventFilter( SDL_Event *event )
 
 		// TODO: Use joyinput funcs, for future multiple gamepads support
 		if( Joy_IsActive() )
-			Key_Event( sdlControllerButtonToEngine[event->cbutton.button], event->cbutton.state );
+			Key_Event( sdlControllerButtonToEngine[event->cbutton.button + 1], event->cbutton.state );
 		break;
 	}
 

engine/platform/sdl/in_sdl.c

@@ -260,7 +260,6 @@ static int SDLash_JoyInit_New( int numjoy )
 		SDL_GameControllerGetProductVersion( gamecontroller ));
 #endif // SDL_VERSION_ATLEAST( 2, 0, 6 )
 	SDL_GameControllerEventState( SDL_ENABLE );
-	SDL_JoystickEventState( SDL_DISABLE );
 
 	return num;
 }