Crashes with OGRE_RESOURCEMANAGER_STRICT

[paroj]

needs porting to work with OGRE_RESOURCEMANAGER_STRICT=2.

The code needs updating to explicitly state the auto-detect group or the known group for retrieval.

see

• https://github.com/OGRECave/ogre/blob/master/Docs/1.10-Notes.md#resourcemanager-strict-mode
• https://github.com/OGRECave/ogre/blob/master/Docs/1.11-Notes.md#cmake-build