afl-fuzz: Fix crash with policy line without ':'

This crash was found by running afl-fuzz. Policy lines without a ':'
were causing strsep(3) to place a NULL in |policy_line|, which was then
being dereferenced.

Bug: None
Test: make tests
Change-Id: I6228a3e4688d4e8641714ec9d10f8cd144dcb5c1
2 files changed