Dolt shell has issues parsing multiple statements in the same line

dolt
```
tmp/main*> select null; select -- comment
-> null;
syntax error at position 20 near 'select'
tmp/main*> select null; select null;
syntax error at position 20 near 'select'
```

MySQL
```
mysql> select null; select -- comment
+------+
| NULL |
+------+
| NULL |
+------+
1 row in set (0.00 sec)

-> null;
+------+
| NULL |
+------+
| NULL |
+------+
1 row in set (0.00 sec)

mysql> select null; select null;
+------+
| NULL |
+------+
| NULL |
+------+
1 row in set (0.00 sec)

+------+
| NULL |
+------+
| NULL |
+------+
1 row in set (0.00 sec)
```

Reproduce the two examples in the Dolt shell, including the semicolon-separated statements and the comment continuation. Trace the shell's statement parsing and compare its behavior with the MySQL examples. Done means both forms execute as separate statements without a syntax error and preserve the expected results.

Written by the indexing model from the issue text.