Close file at the end of runNetwork rather than in stopNetwork in order to avoid a race condition,

also in order to continue tracing the pending network thread activity.
Poll event throttler only in the network thread in order to avoid a race condition.

fdbclient/NativeAPI.actor.cpp

@@ -2555,7 +2555,6 @@ void stopNetwork() {
 
 	TraceEvent("ClientStopNetwork").log();
 	g_network->stop();
-	closeTraceFile();
 }
 
 void DatabaseContext::updateProxies() {

fdbclient/ThreadSafeTransaction.cpp

@@ -591,6 +591,7 @@ void ThreadSafeApi::runNetwork() {
 	}
 
 	TraceEvent("RunNetworkTerminating");
+	closeTraceFile();
 }
 
 void ThreadSafeApi::stopNetwork() {

flow/Trace.cpp

@@ -454,7 +454,9 @@ public:
 	}
 
 	ThreadFuture<Void> flush() {
-		traceEventThrottlerCache->poll();
+		if (TraceEvent::isNetworkThread()) {
+			traceEventThrottlerCache->poll();
+		}
 
 		MutexHolder hold(mutex);
 		bool roll = false;