Description:
------------
Documentation says:
If called without an argument, this function commits the default transaction of the default link.

If you use the function without default link, the script crashes.

Test script:
---------------
$dbh = ibase_connect('10.1.7.100', 'sysdba', 'masterkey');

$query = ibase_prepare($dbh, "UPDATE TBL_USER SET USER_DISPLAY_NAME = 'Koeditz, Martin' WHERE USER_ID = 125");

try {
    $transaction = ibase_trans();
    ibase_execute($query);
    ibase_commit($transaction);
}
catch(Exception $e) {
    ibase_rollback($transaction);
    die($e->getMessage());
}

echo "Everything is fine!";


Expected result:
----------------
If you have to enter a link, the documentation has to be editted.

The program should never crash if the argument is missed.

Actual result:
--------------
The script crashes.
Log output from Apache log:
[Fri Aug 16 11:41:08.021422 2019] [core:notice] [pid 17149] AH00052: child pid 21126 exit signal Segmentation fault (11)