Correct a crash if the length buffer is NULL.
[wine] / dlls / advpack /
drwxr-xr-x   ..
-rw-r--r-- 42 .cvsignore
-rw-r--r-- 308 Makefile.in
-rw-r--r-- 11304 advpack.c
-rw-r--r-- 969 advpack.spec
-rw-r--r-- 5951 reg.c
drwxr-xr-x - tests