[BUG] - can't compile nanovdb_viewer with Optix support

[PaddiM]

Environment

**Operating System: Windows 10 **Version / Commit SHA: af7dae1cff24261f983af0896caf1858762a20d9 **Other: Visual Studio 2019

Describe the bug

RenderlauncherOptix.cpp has a problem with line 809:

auto* node = static_cast<typename nanovdb::TreeNode<nanovdb::FloatTree, NodeLevel>::type*>(nodeAddress);

error is:

cannot deduce auto type. namespace nanovdb has no member TreeNode.

[kmuseth]

looking into this now