the row result is not printed when there is `IF` clause used in the stored procedure when using sql server

Cause of the issue: the current `IfElseBlock{}.Schema()` method returns `nil`, which is used to send the field information over the wire.
Repro in Dolt:
```
mysql> CREATE PROCEDURE p() IF 0 = 0 THEN SELECT 1; END IF#
Query OK, 0 rows affected (0.02 sec)

mysql> CALL p#
Query OK, 1 row affected (0.00 sec)

```

MySQL:
```
mysql> CREATE PROCEDURE p() IF 0 = 0 THEN SELECT 1; END IF#
Query OK, 0 rows affected (0.00 sec)

mysql> CALL p;
-> #
+---+
| 1 |
+---+
| 1 |
+---+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

```