Simplify loop in hash_key().
Simplify loop in hash_key().

This also avoids an underflow if args is empty.

mozilla/sccache,glandium/sccache,glandium/sccache,luser/sccache2,mozilla/sccache,glandium/sccache,luser/sccache2,luser/sccache2,glandium/sccache,luser/sccache2,mozilla/sccache