incorrect row estimates in Connect

Copy the following test case into a file under storage/connect/mysql-test/connect/t:

CREATE TABLE t1 (c INT PRIMARY KEY) ENGINE=CONNECT TABLE_TYPE=CSV;

INSERT INTO t1 VALUES (1),(2);

--query_vertical EXPLAIN SELECT AVG(c) FROM t1

drop table t1;

Observe that the result contains

rows    4

even though the table has only two rows. This becomes important when the number of rows in the table grows large.