Only send cleanup_info messages if VACUUM removes any tuples.

There is no other purpose for this message type than to report
the latestRemovedXid of removed tuples, prior to index scans.
Removes overlooked path for sending invalid latestRemovedXid.
Fixes buildfarm failure on centaur.

src/backend/commands/vacuumlazy.c

@@ -29,7 +29,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.133 2010/04/21 17:20:56 sriggs Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.134 2010/04/21 19:53:24 sriggs Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -274,10 +274,13 @@ vacuum_log_cleanup_info(Relation rel, LVRelStats *vacrelstats)
 	if (rel->rd_istemp || !XLogIsNeeded())
 		return;
 
+	if (vacrelstats->tuples_deleted > 0)
+	{
 		Assert(TransactionIdIsValid(vacrelstats->latestRemovedXid));
 
 		(void) log_heap_cleanup_info(rel->rd_node, vacrelstats->latestRemovedXid);
 	}
+}
 
 /*
  *	lazy_scan_heap() -- scan an open heap relation