Make ResetRemoteTransaction more robust

There's a second issue with ResetRemoteTransaction. The check to remove
the transaction only took into account the state, and not if the
connection was actually part of a list.

src/backend/distributed/transaction/remote_transaction.c

@@ -80,6 +80,7 @@ StartRemoteTransactionBegin(struct MultiConnection *connection)
 
 	/* remember transaction as being in-progress */
 	dlist_push_tail(&InProgressTransactions, &connection->transactionNode);
+	connection->transactionInProgress = true;
 
 	transaction->transactionState = REMOTE_TRANS_STARTING;
 
@@ -865,11 +866,13 @@ ResetRemoteTransaction(struct MultiConnection *connection)
 	RemoteTransaction *transaction = &connection->remoteTransaction;
 
 	/* unlink from list of open transactions, if necessary */
-	if (transaction->transactionState != REMOTE_TRANS_NOT_STARTED)
+	if (connection->transactionInProgress)
 	{
 		/* XXX: Should we error out for a critical transaction? */
 
 		dlist_delete(&connection->transactionNode);
+		connection->transactionInProgress = false;
+		memset(&connection->transactionNode, 0, sizeof(connection->transactionNode));
 	}
 
 	/* just reset the entire state, relying on 0 being invalid/false */

src/include/distributed/connection_management.h

@@ -189,8 +189,12 @@ typedef struct MultiConnection
 	/* information about the associated remote transaction */
 	RemoteTransaction remoteTransaction;
 
-	/* membership in list of in-progress transactions */
+	/*
+	 * membership in list of in-progress transactions and a flag to indicate
+	 * that the connection was added to this list
+	 */
 	dlist_node transactionNode;
+	bool transactionInProgress;
 
 	/* list of all placements referenced by this connection */
 	dlist_head referencedPlacements;