Fix memory allocation mistake

The previous code was allocating more memory than necessary because
the formula used the wrong data type.

Reported-by: Jehan-Guillaume de Rorthais <jgdr@dalibo.com>
Discussion: https://www.postgresql.org/message-id/20191105172918.3e32a446@firost

src/backend/replication/logical/relation.c

@@ -267,7 +267,7 @@ logicalrep_rel_open(LogicalRepRelId remoteid, LOCKMODE lockmode)
 		 */
 		desc = RelationGetDescr(entry->localrel);
 		oldctx = MemoryContextSwitchTo(LogicalRepRelMapContext);
-		entry->attrmap = palloc(desc->natts * sizeof(int));
+		entry->attrmap = palloc(desc->natts * sizeof(AttrNumber));
 		MemoryContextSwitchTo(oldctx);
 
 		found = 0;