GetAssoc issue when 2nd column is null
GetAssoc issue when 2nd column is null

If the second column of the first row happens to be null, ADOdb returned
a one-based array rather than the expected zero-based one.

Resolved by using array_key_exists() instead of isset().

Fixes sourceforge bug #130

paulproteus/ADOdb,andrewnicols/ADOdb,ipso/ADOdb,pyscht/ADOdb,andrewnicols/ADOdb,azghanvi/ADOdb,paulproteus/ADOdb,azghanvi/ADOdb,ipso/ADOdb,pyscht/ADOdb