Missing break in switch-case.

Fixed issue resulting in segfault and sometimes incorrect result set mapping.

To reproduce before you merge...

_Incorrect result map:_
```
var sqlanywhere = require('sqlanywhere');
var conn = sqlanywhere.createConnection();
conn.connect({host: 'xxxx', uid: 'xxxx', pwd: 'xxxx'}, function() {
    console.log(conn.exec('select 1 as a, 2 as b, null as c, 1 as d'));
    conn.disconnect();
});
// Prints [ { a: 1, b: 2, c: 1, d: null } ].....Note the null is associated with "d" now.
```

_Segfault_
```
var sqlanywhere = require('sqlanywhere');
var conn = sqlanywhere.createConnection();
conn.connect({host: 'xxxx', uid: 'xxxx', pwd: 'xxxx'}, function() {
    console.log(conn.exec('select 1, null, null'));
    conn.disconnect();
});
```

I tried running these tests against SQL Anywhere 10.0.1.3960 and 12.0.1.3873.