Fix bogus MaxAllocSize check in logtape.c.

Reported-by: Peter Geoghegan
Discussion: https://postgr.es/m/CAH2-Wz=NZPZc3-fkdmvu=w2itx0PiB-G6QpxHXZOjuvFAzPdZw@mail.gmail.com
Backpatch-through: 13

src/backend/utils/sort/logtape.c

@@ -491,7 +491,7 @@ ltsReleaseBlock(LogicalTapeSet *lts, long blocknum)
 		 * If the freelist becomes very large, just return and leak this free
 		 * block.
 		 */
-		if (lts->freeBlocksLen * 2 > MaxAllocSize)
+		if (lts->freeBlocksLen * 2 * sizeof(long) > MaxAllocSize)
 			return;
 
 		lts->freeBlocksLen *= 2;