quiet gcc 4.4.7 warning about saveptr use before initialization

The recent change to use strtok_r causes a build warning with this older
gcc version, so initialize saveptr to NULL to quiet the compiler and
unbreak the build. There was no warning with gcc 4.7.2 that I
originally tested with.

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>