Bugfix/fix snapshot reloading crash (#979)

* The original code asserts when reloading a snapshot because it makes an assumption that the worker stats will be present.  This change removes the assumption.

* update CHANGELOG.md

CHANGELOG.md

@@ -27,6 +27,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Singletons authority and state resumes correct when reconnecting servers to snapshot.
 - Fixed a crash when retrying reliable RPCs with UObject arguments that got destroyed before the RPC was retried.
 - Fixed path naming issues in setup.sh
+- Fixed assert/crash in SpatialMetricsDisplay that occurred when reloading a snapshot.
 
 ### External contributors:
 

SpatialGDK/Source/SpatialGDK/Private/Utils/SpatialMetricsDisplay.cpp

@@ -182,16 +182,15 @@ void ASpatialMetricsDisplay::Tick(float DeltaSeconds)
 
 		for (const FWorkerStats& OneWorkerStats : WorkerStats)
 		{
-			const float TimeSinceUpdate = CurrentTime - WorkerStatsLastUpdateTime[OneWorkerStats.WorkerName];
-
-			if (TimeSinceUpdate > DropStatsIfNoUpdateForTime)
+			if (ShouldRemoveStats(SpatialNetDriver->Time, OneWorkerStats))
 			{
 				WorkerStatsToRemove.Add(OneWorkerStats);
 			}
 		}
 
 		for (const FWorkerStats& OneWorkerStats : WorkerStatsToRemove)
 		{
+			WorkerStatsLastUpdateTime.Remove(OneWorkerStats.WorkerName);
 			WorkerStats.Remove(OneWorkerStats);
 		}
 	}
@@ -234,3 +233,16 @@ void ASpatialMetricsDisplay::Tick(float DeltaSeconds)
 
 	ServerUpdateWorkerStats(SpatialNetDriver->Time, Stats);
 }
+
+bool ASpatialMetricsDisplay::ShouldRemoveStats(const float CurrentTime, const FWorkerStats& OneWorkerStats) const
+{
+	const float* LastUpdateTime = WorkerStatsLastUpdateTime.Find(OneWorkerStats.WorkerName);
+
+	if (LastUpdateTime == nullptr)
+	{
+		return true;
+	}
+
+	const float TimeSinceUpdate = CurrentTime - *LastUpdateTime;
+	return TimeSinceUpdate > DropStatsIfNoUpdateForTime;
+}

SpatialGDK/Source/SpatialGDK/Public/Utils/SpatialMetricsDisplay.h

@@ -59,6 +59,7 @@ class SPATIALGDK_API ASpatialMetricsDisplay :
 	UFUNCTION(CrossServer, Unreliable, WithValidation)
 	virtual void ServerUpdateWorkerStats(const float Time, const FWorkerStats& OneWorkerStats);
 
+	bool ShouldRemoveStats(const float CurrentTime, const FWorkerStats& OneWorkerStats) const;
 	void DrawDebug(class UCanvas* Canvas, APlayerController* Controller);
 
 	struct MovementCorrectionRecord