Fix for message on resource-only non-DITA files (e.g., png). #1597
Added handling of inherited processing-role #1597
Corrected markup per feedback from Jarno
Merge pull request #1624 from drmacro/hotfix/1.8.4

This is my fix for 1597. It appears to correctly handle the case where a topicref or any ancestor is resource-only. I tested with my client's failing real document.