nlist: Check whether the nl argument is not NULL

This prevents programming errors.

Reported-by: Daniel Hodson <daniel@elttam.com.au>
Based-on-patch-by: Daniel Hodson <daniel@elttam.com.au>
Signed-off-by: Guillem Jover <guillem@hadrons.org>

man/nlist.3bsd

@@ -72,7 +72,10 @@ The last entry in the list is always
 The number of invalid entries is returned if successful; otherwise,
 if the file
 .Fa filename
-does not exist or is not executable, the returned value is \-1.
+does not exist or is not executable,
+or the nl pointer is
+.Dv NULL ,
+the returned value is \-1.
 .Sh SEE ALSO
 .Xr elf 5
 .Sh HISTORY

src/nlist.c

@@ -258,6 +258,10 @@ nlist(const char *name, struct nlist *list)
 {
 	int fd, n;
 
+	if (list == NULL) {
+		errno = EINVAL;
+		return (-1);
+	}
 	fd = open(name, O_RDONLY, 0);
 	if (fd < 0)
 		return (-1);