Don't report stats in LogicalRepApplyLoop() when in xact.

pgstat_report_stat() is only supposed to be called outside of transactions. In
5891c7a8ed I added a pgstat_report_stat() call into LogicalRepApplyLoop()'s
timeout branch. While not commonly reached inside a transaction, it is
reachable (e.g. due to network bottlenecks or the sender being stalled / slow
for some reason).

To fix, add a !IsTransactionState() check.

No test added because there's no easy way to reproduce this case without
patching the code.

Reported-By: Erik Rijkers <er@xs4all.nl>
Discussion: https://postgr.es/m/b3463b8c-2328-dcac-0136-af95715493c1@xs4all.nl

src/backend/replication/logical/worker.c

@@ -2883,9 +2883,14 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
 
 			/*
 			 * Force reporting to ensure long idle periods don't lead to
-			 * arbitrarily delayed stats.
+			 * arbitrarily delayed stats. Stats can only be reported outside
+			 * of (implicit or explicit) transactions. That shouldn't lead to
+			 * stats being delayed for long, because transactions are either
+			 * sent as a whole on commit or streamed. Streamed transactions
+			 * are spilled to disk and applied on commit.
 			 */
-			pgstat_report_stat(true);
+			if (!IsTransactionState())
+				pgstat_report_stat(true);
 		}
 	}