fix: null-safe budget release in LoadAssetBundleSystem

The pooled StreamableLoadingState can be recycled (budget disposed and
nulled via the pool actionOnRelease) if the promise is forgotten or
cancelled while the detached flow is mid-await. Releasing the budget with
!. would NRE in that window, so guard with ?. to match how the budget is
treated everywhere else in the flow.

Author: alejandro-jimenez-dcl

Explorer/Assets/DCL/Infrastructure/ECS/Unity/StreamableLoading/AssetBundles/LoadAssetBundleSystem.cs

@@ -96,7 +96,9 @@ protected override async UniTask<StreamableLoadingResult<AssetBundleData>> FlowI
             }
 
             // Release budget now to not hold it until dependencies are resolved to prevent a deadlock
-            state.AcquiredBudget!.Release();
+            // Null-safe: the pooled state can be recycled (budget disposed and nulled) if the promise is
+            // forgotten/cancelled while this detached flow is mid-await
+            state.AcquiredBudget?.Release();
 
             // if GetContent prints an error, null will be thrown
             if (assetBundle == null)