Discrepancy between UV channel size value and the actual values in the buffer

[carmenfan]

Description

This is completely my fault, with a commit in the last release; 29edc9e

If the byte count of the UV channels is 0, we stopped writing a buffer entry for the non existent buffer.

What I overlooked was the UV channel count value slightly above this: 29edc9e#diff-8362648406f916c57c5c876e6cda36445ce2de179cc288169c17b503d9f17fbfL457

So we ended up with inconsistent values, where the channel size could be 1 when there is no buffer, causing meshes that has no texture to be grouped together with a textured group in the mesh batching process.

Steps to replicate

Upload these files: https://asitesol.sharepoint.com/:f:/s/3DRepoTeamFolder/EqCt1Y2KtTRFogU39zy0RkcBSTp61pASYLI9HELV_ZxDPA?e=1NYyse

Current Behaviour

in 5.8.1 - this fails during unity when we are reorganising the mesh for bundle generation

Expected Behaviour

should upload successfully (as per 5.6.0)