Fix Regression: null UWorld deref in CesiumGaussianSplatSubsystem::Tick

[UmarMukhtar0039]

Moved IsValid(pWorld) above the IsNetMode(NM_DedicatedServer) deref so a null result from GetPrimaryWorld() no longer crashes InternalGetNetMode. Restores the v2.24.1 ordering inverted by commit 05fce68.

Fixes #1841

Description

Restore the IsValid(pWorld) check above the pWorld->IsNetMode(NM_DedicatedServer) deref in UCesiumGaussianSplatSubsystem::Tick. This is the ordering that shipped in 2.24.1 (UE 5.7 Marketplace) and was inadvertently regressed in commit 05fce68 ("close to working [skip ci]") during the recent Niagara/Gaussian-splat refactor.

This fixes #1841 and also Play in Standalone in Unreal projects with Cesium enabled.

Issue number or link

#1841 and also Play in Standalone crash in Unreal projects with Cesium enabled.

Author checklist

• I have submitted a Contributor License Agreement (only needed once).
• I have done a full self-review of my code.
• I have updated CHANGES.md with a short summary of my change (for user-facing changes).
• [ ] I have added or updated unit tests to ensure consistent code coverage as necessary.
• [ ] I have updated the documentation as necessary.

Remaining Tasks

NA

Testing plan

• Make a fresh project in Unreal and enable CesiumForUnreal
• Login to Cesium Ion
• Bring in the 3D tiles and start the project in Standalone.

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[j9liu]

Thank you for opening this @UmarMukhtar0039! The fix looks good, sorry that I ended up breaking things 😅

If you could update CHANGES.md with an entry about this bugfix, this PR will be good to go!

[UmarMukhtar0039]

@j9liu This is ready

[j9liu]

Thanks @UmarMukhtar0039! I confirmed that this does fix the crash in standalone game mode.

It seems that Gaussian splats don't show up in the standalone window, unfortunately, but that can be addressed as a separate issue. I'll wait for CI to pass before merge. Thanks again!

[UmarMukhtar0039]

Hi @j9liu I also noticed that. I am pretty sure it has to do with how we get the world context - the function GetPrimaryWorld() the code early exits if we are not in the editor. I'll see what I can do in my free time.