DV: Fix REPLACE tiles never being selected in some cases

[Kaapp]

When we produce mesh tilesets, we usually end up creating a fake root tile to hold many children. This tile will have the ADD refinement strategy which meant that we would display the mesh properly.

However, in some cases, we end up with a singular root tile if the file is particularly simple (as seen here). In this case, the root tile has a REPLACE refinement strategy, and so we will add a Tile3D to the selectedTileGroups rather than a TileGroup3D. This means that our replacement handling code will get stuck and throw the warnings that we've seen on a few projects. This would result in us downloading but never actually displaying the child tiles content (as it would never be selected properly).

Instead, we only set the selectedTileGroups values for non-REPLACE tiles.

Before:

After:

[Gmadges]

nice catch

[Rennzie]

Nice one.