[MPlayer-dev-eng] [PATCH] Fix key_down_event SEGFALT

I discovered by messing around that using key_down_event with a large random value (ex SPACE | MP_NO_REPEAT_KEY) can cause a segfalt. I found the problem to be that isprint is only defined for values in the range of an unsigned char and the value EOF. The patch adds a simple check before isprint in mp_input_get_key_name to make sure the value is in isprint's range.