[BusyBox] skip_whitespace.c can segfault

[Tito]

Hi to all,
I noticed that the bb_skip_whitespace() function can
segfault if the argument passed is NULL as can 
easily be demonstrated by this example:

#include <ctype.h>
#include <stdio.h>

/*#include "libbb.h"*/


extern const char *bb_skip_whitespace(const char *s)
{
	while ( isspace(*s)) {
		++s;
	}

	return s;
}

int main(int argc, char **argv)
{
	bb_skip_whitespace(NULL);
	return 0;
} 

root at localhost:/dev/pts/1:/rep/busybox-1.00-pre8/libbb# ./test
Segmentation fault (core dumped)

I can't say if this is a treat for an experienced programmer,
but it could be fixed by modifying *bb_skip_whitespace(const char *s) to

extern const char *bb_skip_whitespace(const char *s)
{
	while ( s &&  isspace(*s)) {
		++s;
	}

	return s;
}

the increase in size is not so much:
root at localhost:/dev/pts/1:/rep/busybox-1.00-pre8/libbb# size skip_whitespace.o
   text    data     bss     dec     hex filename
     29       0       0      29      1d skip_whitespace.o
root at localhost:/dev/pts/1:/rep/busybox-1.00-pre8/libbb# size skip_whitespace.o
   text    data     bss     dec     hex filename
     33       0       0      33      21 skip_whitespace.o
root at localhost:/dev/pts/1:/rep/busybox-1.00-pre8/libbb#

The gurus will know whether it is worth to fix it or not.   ;-)

Ciao,
Tito