Don't call CheckAttributeType() with InvalidOid on dropped cols

If CheckAttributeType() is called with InvalidOid, it performs a bunch
of pointless, futile syscache lookups with InvalidOid, but ultimately
tolerates it and has no effect. We were calling it with InvalidOid on
dropped columns, but it seems accidental that it works, so let's stop
doing it.

Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://www.postgresql.org/message-id/93ce56cd-02a6-4db1-8224-c8999372facc@iki.fi
Backpatch-through: 14

src/backend/catalog/heap.c

@@ -504,11 +504,15 @@ CheckAttributeNamesTypes(TupleDesc tupdesc, char relkind,
 	 */
 	for (i = 0; i < natts; i++)
 	{
-		CheckAttributeType(NameStr(TupleDescAttr(tupdesc, i)->attname),
-						   TupleDescAttr(tupdesc, i)->atttypid,
-						   TupleDescAttr(tupdesc, i)->attcollation,
+		Form_pg_attribute attr = TupleDescAttr(tupdesc, i);
+
+		if (attr->attisdropped)
+			continue;
+		CheckAttributeType(NameStr(attr->attname),
+						   attr->atttypid,
+						   attr->attcollation,
 						   NIL, /* assume we're creating a new rowtype */
-						   flags | (TupleDescAttr(tupdesc, i)->attgenerated == ATTRIBUTE_GENERATED_VIRTUAL ? CHKATYPE_IS_VIRTUAL : 0));
+						   flags | (attr->attgenerated == ATTRIBUTE_GENERATED_VIRTUAL ? CHKATYPE_IS_VIRTUAL : 0));
 	}
 }