Description:
------------
I work with this environment:
* OS: Linux
* Web server: Apache 2.0
* DB server: Microsoft SQL server (7.0 or 2000)
* PHP 5.1.2

I execute a query with odbc_query() function. when the first record result has a NULL value in a field, the next record that doesn't has a NULL value in the same field doesn't return the correct value. It returns unrecognizable chars. 

Reproduce code:
---------------
$res = odbc_exec ($bd, "SELECT Id, Num, Obs FROM publicacions");
odbc_result_all ($res);

-----------

$res = odbc_exec ($bd, "SELECT Id, Num FROM publicacions");
while (odbc_fetch_row ($res))
     echo odbc_result ($res, "Id")." ".odbc_result ($res, "Num")." ".odbc_result ($res, "Obs")."<br>";



Expected result:
----------------
Id   Num   Obs
--------------
1    NULL  NULL
2    NULL  comment
3    23    NULL
4    45    aaaaa
5    NULL  bbbb
6    12    ccccc


Actual result:
--------------
Id   Num   Obs
--------------
1    NULL  NULL
2    NULL  ??H@??H@
3    ??H@  NULL
4    45    aaaaa
5    NULL  bbbb
6    12    ccccc