Fix exception when exiting Program Settings menu and listcount==0:

strlen() line 78
_strdup(const char * 0xcccccccc) line 48 + 9 bytes
show_bbslist(char * 0x00000000, int 0x00000000) line 1872 + 35 bytes
CIOLIB_main(int 0x00000001, char * * 0x01243760) line 1288 + 20 bytes
sdl_run_main(void * 0x0012feb8) line 302 + 25 bytes