Insteon: Fix Bug in PLM Sanity Check Which Caused Crash on X10 Messages

Fix issue identified by Marc

http://misterhouse.10964.n7.nabble.com/Insteon-IOLinc-Support-Draft-Done-tp17944p17950.html
Merge pull request #180 from krkeegan/fix_issue_83

Insteon: Fix Bug in PLM Sanity Check Which Caused Crash on X10 Messages