fix freadptr to work with ungetc on all uClibc configs This was noticed at https://bugs.busybox.net/show_bug.cgi?id=4099 where GNU coreutils cut fails like: $echo '3:0:0:' | cut -d : -f 2 30 The reason is because GNU cut uses ungetc(), and that wasn't handled appropriately on uClibc when __UCLIBC_HAS_STDIO_GETC_MACRO__ is not defined. * lib/freadptr.c (freadptr): Return NULL if there are ungotten chars. In this case freadseek() will iterate again to process the ungotten character.