Fix RELCACHE_FORCE_RELEASE issue

Introduced by 83fd4532.  To fix, the
tuple descriptors need to be copied into the current memory context.

Discussion: https://www.postgresql.org/message-id/04d78603-edae-9243-9dde-fe3037176a7d@2ndquadrant.com

src/backend/replication/pgoutput/pgoutput.c

@@ -305,7 +305,8 @@ maybe_send_schema(LogicalDecodingContext *ctx,
 
 		/* Map must live as long as the session does. */
 		oldctx = MemoryContextSwitchTo(CacheMemoryContext);
-		relentry->map = convert_tuples_by_name(indesc, outdesc);
+		relentry->map = convert_tuples_by_name(CreateTupleDescCopy(indesc),
+											   CreateTupleDescCopy(outdesc));
 		MemoryContextSwitchTo(oldctx);
 		send_relation_and_attrs(ancestor, ctx);
 		RelationClose(ancestor);