On UP system, make sure that mbuf chain is not empty before accessing it.
tree9f141a49b046eaa53302b5579c09cbcbc46d3c57
-rw-r--r-- 6909 COPYRIGHT
-rw-r--r-- 8256 Makefile
-rw-r--r-- 34081 Makefile.inc1
-rw-r--r-- 27219 Makefile_upgrade.inc
-rw-r--r-- 2613 README
-rw-r--r-- 384 README.amd64
-rw-r--r-- 9341 UPDATING
drwxr-xr-x - bin
drwxr-xr-x - contrib
drwxr-xr-x - crypto
drwxr-xr-x - etc
drwxr-xr-x - games
drwxr-xr-x - gnu
drwxr-xr-x - include
drwxr-xr-x - kerberos5
drwxr-xr-x - lib
drwxr-xr-x - libexec
drwxr-xr-x - nrelease
drwxr-xr-x - sbin
drwxr-xr-x - secure
drwxr-xr-x - share
drwxr-xr-x - sys
drwxr-xr-x - test
drwxr-xr-x - tools
drwxr-xr-x - usr.bin
drwxr-xr-x - usr.sbin