fix: add safety against no ctxTexture

[pawelocode]

This change fixes an issue seen on specific devices since V2.20.0.

Im not sure if this is the best approach but hopefully this PR starts the conversation

[CLAassistant]

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[yananazarenko417]

experiencing the same issue on both of my Samsungs. The renderer on 2.20.0 seems to be reading the texture coordinates even if it undefined / failed to load texture causing app crashes (black screen)

[wouterlucas]

does that mean the texture creation is really slow on those devices? Does the rendering have a 1 or 2 frame artifact and then auto corrects or is this always going to be broken (ie the texture never got created versus its slow)?

[michielvandergeest]

this PR originated from an issue that we could only reproduce on the slowest Sky Q device in combination with compressed textures (which may take longer to download because of the file size). So some slowness on devices could be responsible for this error

@pawelocode can you comment on the following question: Does the rendering have a 1 or 2 frame artifact and then auto corrects or is this always going to be broken (ie the texture never got created versus its slow)?

when you tested did the image ultimately correct itself? or remained broken forever? Even with this fix

[pawelocode]

Hey Everyone so when I tested this I manually I made one of the low opacity fade asset fail and what I saw:
On the Q device the missing asset became a white rectangle (covering all content underneath) - this was the same on the previous version of the renderer.
The difference on the latest version is that nothing rendered as the app crashed without the safety

On the desktop browser just the asset was missing and the content in that area is still visible.
So in this state the PR just fixes the crash behaviour

[yananazarenko417]

just to add to my previous comment: the app fails even on the high end device (v 2.20), so I am not sure it has anything to do with the slowness of the texture creation. It does not happen on all devices though, I had the app failing completely (black screen) on 2 Samsungs but not on LG. It does clearly happen as soon as I have an asset that has failed to load in the viewport. The app fails cause it still tries to read the txCoordX1, although the texture is undefined. So clearly some safety missing
Works just fine and never fails on all the versions before

didn't test the fix from this MR yet

[wouterlucas]

OK - would be good to find the root cause instead of adding a safety that only prevents the pipeline from crashing.
Agree that's likely a good long term stability thing to have, but this might mask uncovering what the root cause is.

@pawelocode I'll reach out on slack to see if we can debug this together with @jfboeve