Issue properly WAL record for CID of first catalog tuple in multi-insert

Multi-insert for heap is not yet used actively for catalogs, but the
code to support this case is in place for logical decoding.  The
existing code forgot to issue a XLOG_HEAP2_NEW_CID record for the first
tuple inserted, leading to failures when attempting to use multiple
inserts for catalogs at decoding time.  This commit fixes the problem by
WAL-logging the needed CID.

This is not an active bug, so no back-patch is done.

Author: Daniel Gustafsson
Discussion: https://postgr.es/m/E0D4CC67-A1CF-4DF4-991D-B3AC2EB5FAE9@yesql.se

src/backend/access/heap/heapam.c

@@ -2191,6 +2191,14 @@ heap_multi_insert(Relation relation, TupleTableSlot **slots, int ntuples,
 		 * Put that on the page, and then as many other tuples as fit.
 		 */
 		RelationPutHeapTuple(relation, buffer, heaptuples[ndone], false);
+
+		/*
+		 * Note that heap_multi_insert is not used for catalog tuples yet,
+		 * but this will cover the gap once that is the case.
+		 */
+		if (needwal && need_cids)
+			log_heap_new_cid(relation, heaptuples[ndone]);
+
 		for (nthispage = 1; ndone + nthispage < ntuples; nthispage++)
 		{
 			HeapTuple	heaptup = heaptuples[ndone + nthispage];